Oh noes, registry roes! Even as an experienced user, I rarely directly modify my registry, it's just too dangerous in the Windoze world.
The first thing I do on my sister's laptop which has crappy specs (1.6 AMD Semipron [just like a celeron], with 256 MB RAM) is turn off the extras, I switch back to classic style on the start menu and desktop theme. You can do this by right clicking the desktop and selecting properties and right clicking the start menu and clicking properties.
It's a tiny change but seems to speed things up. Also, I run it without AV or a Firewall (other than Windows) even though it's permanetly connected to the net for the little bit of net surfing that my sister does, I'm really not that worried. Plus, I'm confident in my ability to clean out the crap or at the worst format and reinstall windows.
I also recommend this handy little tool:
cCleaner which cleans out all your temporary files and junk with one click!
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