you can, its just extremely slow, for the ram that it has. its specs are completely good, except for the ram: 733mhz celeron, 64mb ram, 8gb hdd. with a modded box, it is possible(and runs pretty good) with DSL, 95, 98, 2kprosp4(havent tried xp tho)
since i gave up on xp, i thought of another thing: that hdd is ok, since the box is fried, so i went on a quest to unlock it, and i actually succeded(without using the xbox what so ever, just the computer)
and, for the ram upgrade, they are avail, but you cant do it urself unless you are extremely good at soldering (i mean micro, like the type of skils to add more ram to a video card..which it realy is)