I don't actually have Powerslave but with most other Build engine games usually the first thing you'll need is NOLFB. You can get that here http://advsys.net/ken/build.htm
Put NOLFB.COM in the game's directory then open the game's .cfg file and set screenmode=2 or use the setup program to select VESA 2.0.
For VDMSound to work, make sure you setup the sound to use blaster address=220, DMA=1 and IRQ=7.
You might want to just make a batch file to launch the game - should look something like this
@echo off
nolfb.com
dosdrv
pause
(game's .exe name here)
Hope this helps.
Edit: I just had a go at it and although I got it working initially, the game crashes as soon as I round the first corner. Tried all the usual tricks like memory dropdowns, w95 mode, fullscreen etc. but still no luck. Sorry it's not working properly in XP here either. 🙁