For a short term improvement a good core2duo would work but the only way I would do a Core2Duo is buying used from a top rated seller on Ebay
who has a good DOA policy
Buying a new retail Core2Duo just doesnt make sense
Some of the good new Core2Duo cost almost as much as an AMD mobo/cpu
combo
in your future build
Might be able to use case depending on form factor that Lenovo used
Some OEMs use BTX cases which are hard to reuse
Hard drive (if it is big enough for you) and DVD/CD would be reusable
decent power supplies have gotten cheap with sales so replace it with a
Corsair,Seasonic,Antec
the ram is probably DDR2-800-might be reusable-better off upgrading
if budget allowed
Look up toms systems builder marothon systems to get an idea
of good components for the money
the one thing that makes sense is upgrading your video card
since that can be carried to new build
post more detailed specs and budget in graphics section
and toms members will bore you with video card
recommendations LOL
if your computer has a standard size power supply
than a video card and PSU combo upgrade would be good
and used in later build
I hope this made sense
it is 2 am where I am at LOL