Kicking the dust off my noggin getting windows to work is a real pain in the butt. my best was 3 in one box worked great in dos could only get 2 of them to get along and with windows no matter the fight the onboard one fought with the soundblasters. just double check the settings. there are separate sound blaster settings in windows with in creatives installed software. the card not being pnp aka plug and pray should have nothing to do with long as all the right drives and ports ,irq's dma channels are conflict free it should work fine. win 95 and 98se never gave me fits as for as the sounds cards just everything else now 2000pro and xp they brought just fits outright.
Did some snooping around found below posted at wiki.

Capacitor and sound quality issues
As many Sound Blaster 16s are now well over 20 years old, many cards suffer from symptoms related to aging capacitors, ranging from muffled or distorted output to the cards working improperly. In addition, with regard to the amplifier design on most boards Creative did not strictly follow the datasheets' recommendations on capacitor uF values, negatively impacting the amplified output's sound quality. Replacing the capacitors with fresh ones of the recommended values can noticeably improve both amplified and line-level audio quality, in addition to restoring proper operation.
On many TEA2025-based boards, Creative used 47uF capacitors for the amplifier's inverting input DC decoupling (connecting the Feedback pins on the amplifier's pin-out), whereas the datasheet recommended 100uF units against an increase in low-pass cutoff.[7] In addition, Creative installed 1 uF input decoupling capacitors on the TEA2025's inputs, which according to the datasheet should have been 0.22uF units and were only necessary when a volume control slider or knob was present, but were installed regardless if the volume knob was present. (These capacitors may be replaced with short jumper wires if no volume control slider or knob is present.) Finally, Creative used polarized capacitors where non-polarized capacitors should have been used.
On boards that use the TDA1517 amplifier, Creative used 470uF capacitors for the outputs where the TDA1517 datasheet schematic suggested 1000uF units.[8] Depending on the board, an undervalued capacitor for supply voltage rejection (connecting pin 3 of the TDA1517 to ground) may also have been used; the datasheet recommends a 100uF unit for this application. The two output capacitors have a DC voltage present, so polarized units may be used.
Sound Blaster 16 sound cards with the CT1747 chipset frequently have the internal preamplifier gain set too high, causing clipping and crackling in the output that wasn't present on sound cards built using the larger and less integrated CT1746B chip. Changing the mixer levels has no effect on the clipping; the only way to fix this would be to decrease the preamplifier's gain level.
Some Sound Blaster 16 cards made after 1992 may have grounding loops and overall less effective filtering on the +5 volt and +12 volt DC traces coming from the ISA bus. A symptom of these cost-reduced designs is an audible hiss or buzz which is present even when the card is not playing any sounds, which may affect both amplified and line-level outputs. Fixing these problems may not be trivial depending on the card's design.

You made go check both of my dos boxes one hasn't been run since April the other mid October was looking for files and couldn't find them. I have stuff in other machines that no longer serve useful for everyday stuff. Nothing but storage for loaded up hardrives. Ended up finding what i wanted in the home automation control computer. <-- This fool is doing it old school rs232 interface.

Back to the issue at hand the card works in dos fully when you run the dos testing software right (you get all sounds and music)? When you say it's busy in windows what does the popup actually say? Seen insufficient memory ,out of range before my guess is the sb16 and the on board sound possibility a com port conflict. Have experienced windows and it's silly butt trying to share irq #2 meanwhile force the soundcard to irq7. Being an old compaq with a riser tree they may have done some funny bs to get all the on board features to work. Did this machine when new support phone answering and have phone jack headers on mainbaord for the modem? Yes this was a hot idea at one time if so you may be fighting a no win battle. With a pnp card or not and being isa or pci version may not matter. These mainboards were custom ones using soft modems ie no controller chip so resource sharing was common in these machines. So adding a soundblaster to it may not be possable.

My suggestions before throwing in the towel one remove onboard sound drives form windows you my have to force a disable this on windows and it will not like it seeing it loves to install everything without asking. Then get mainbaord model number and machine model number do some looking on line and hope a angelfire or geocites sever is still kicking out there having old board posts about this very issue. Start digging around and see if you still have the factory recovery cd this would have the right drives for any on boards stuff. If there is a way my guess is you had to run a batch file to software disable the onbaord card over and above telling bios to ignore it.

Oh by the way you have to dec 14th to relive you aol instant messenger aka aim days they are killing it.