If you can run in a small window, you're not running on the voodoo since v1 and v2 are ''full screen only''.
Also the default settings for the voodoo's is always a little bright (too me) so that is a way i can see the voodoo is running. When running a Glide executable you'll see a 3dfx splash screen so you'll know the voodoo is taking over.
When you pair it with a S3 card or something like that you'll know.....you will certainly know.... since the voodoo will be fast and the s3 mega slow.
asus tx97-e, 233mmx, voodoo1, s3 virge ,sb16
asus p5a, k6-3+ @ 550mhz, voodoo2 12mb sli, gf2 gts, awe32
asus p3b-f, p3-700, voodoo3 3500TV agp, awe64
asus tusl2-c, p3-S 1,4ghz, voodoo5 5500, live!
asus a7n8x DL, barton cpu, 6800ultra, Voodoo3 pci, audigy1