Looks like I'm gonna make the first useful post here;
If the computer is of no particular importance to you or others, then just stick with Windows XP. There isn't any point switching over until actual problems will arise, which they haven't yet. More to the point, you Dell may not be able to run more up to date versions of Windows; Just because Windows update checker said you theoretically can "run" windows 7, doesn't mean it'll do so well; I tried to do so on my Pentium III 1GB machine with a Geforce 6200 and it ran alright, aside from the 6 minute loading time, and any window opening in about 15 seconds of clicking on it.
As for Linux, well, It's an alternative for windows vista/7/8 for when "problems arise" and you have to switch over. Again, depending on the hardware you may want to use Linux instead of windows.
P.S. I'm using a windows XP machine to post this right now, and it works perfectly well. In my eyes, the end of support was only there to scare XP users into buying more of Windows' products.
