Core 2 Duo E4600, any good?
Yup, fine. One of the E6xxx would be a tad finer. In my neck of the woods an E6600 costs about 40% more than an E4600 for a system maybe 10% faster in normal use, so I'd go with the E4600. Since you're moving from 3000XP either would provide a good speed bump. If you're a gamer, definitely the slower CPU and spend the difference on a better graphics card. If you're not a gamer, well, still the E4600 :-)