Disclaimer: it's also a long time since I configured multibooting os's, so take my advice with a grain of salt.
Firstly, the extra RAM will definitely be helpful, and worthwhile, if you don't have to pay too much. 256 is a pretty small amount these days.
You should also consider other distros, like Xubuntu, which will feel more responsive. There's a number of distributions targeted at producing a more responsive OS.
For your boot loader to work without the need for manual editing, you may need to install the OS's in a particular order. I can't remember the details about this, but seem to recall the *ubuntu installer liked to have XP installed first, or the boot loader would not be properly updated with a boot entry for it.
Get ready for lots of reading with Linux distros (specially if you want to use more than one, as there are some important differences which may not be immediately apparent). At least become comfortable with manual editing for the boot loader, as it is handy even for updates of a single Linux distro (you may get unwanted automatic entries for outdated kernals, but can't remember the details of this). It may also be necessary for debugging boot issues.
Be prepared for hassles with drivers. Again, more reading to be done.
Hope that helps. I do find it useful to run Linux at home, though I don't need to do so very often.
Oli
