The actual issue with 98SE is the video card being addressed as memory. Like most things in 9x, the video card is written to/read from with a memory location and in this case, the location begins at the 1GB mark. Everything above 640KB all the way up to 1GB is reserved for system memory, then the video card uses the next bit of address space, then more components and so on. Sadly, as far as I know, this is hard coded into the OS and cannot be changed. For this reason, you should be able to run anything below 1GB (or at 1GB with video in 640x480 and 256 colors because this mode can be handled within the base 640K of RAM,) but not above. It's been almost a year since I've encountered this problem, but I remember it giving me fits until I realized everything worked perfectly fine with 512 or 768 meg of memory and I went poking around support.microsoft.com for some answers.
Suggestion, use XP or stick with 512. Besides, how are you ever going to fill up a gig of RAM before 98 crashes anyway?
Oh yeah, to be "on topic," this was a pretty sweet deal while it lasted