First unless you have a 64-bit version of XP you will not see more then 2GB of that 4GB of memory. With the /3GB switch you might get 2.5+ GB (If your computer is running down hill with the wind at its back).

Second, maya crashes (as far as I know) do not save any associated folders and really should not cause any folders to go missing.

Sometimes maya will attempt to save a copy of the scene file in Documents and Setting\<user>\Local Settings\Application Data\Temp. Look for *.mb or *.ma.

But this is the extent of it. I don't believe it will make any effort to backup folders with content being used. This sounds more like a hard drive failure than something a maya crash would cause.