Just an observation, but if there are other users out there like C²zero paying similar prices for computer hardware that C²zero paid for the SiS video card, then that may be why you cannot afford new hardware. This observation is not meant to be a slam on C²zero, but, folks, you may want to shop around or ask your "geek" friends about where to get hardware and software. Sixty-four (64) MB cards were going for as low as $200 last year at this time.
With respect to my experience with OBNT, I'm nearing my third renewal for the suite of products. I've used the software on machines ranging from an AMD

-2 300 with 64 MB of RAM to my current machine, which is an AMD Athlon 850 with 512 MB of RAM. I only recently purchased XP. Prior to it, I used ODNT on an AMD

-2 450 running 98, 98SE and WinME. As I upgraded versions of windows, I used WB 1.x and alpha/beta versions of DX. I can honestly say I didn't have any major problems with any system configuration.
As many have said here, there were the occational skins that didn't play nice, but overall my system performed as expected. Ah, "as expected." Yes, perhaps that is the issue: Users load their systems up with programs then throw ODNT in the mix...not in all cases, but I cannot believe that people using ODNT are "casual users" who don't also try other software that's out at download.com, tucows.com or nonags.com.
Solution: Make two different versions of the suite and apps within the suite: "Windowblinds Classic" and "Windowblinds 2002" for example. The "2002" nomenclature would increment as makes sense, "IP 2002", "ODNT 2003", "DX 2004", etc. If a user attempts to install the "2002" version of the software on a pre-NT kernel machine, they get a warning about the 2000/XP version potentially having unwanted effects on Win9x versions. Furthermore, notify your customer base that further development of enhancements for the "Classic" version will cease on "blah blah" date, but that you will continue to support the software (tech support, bug fixes, forums, whatever). You continue to support the product and many will continue to skin for it - just no further enhancements.
As far as full-blown product support, I think Stardock should follow the lead of MS. I'm not an MS "fan" by any means, but 2000 and XP have features that 9x will never support. Stop supporting the "Classic" version when MS is no longer supporting the OS for which it is intended.