typically..... Intel® Core™ 2 Extreme processor/ Intel® Core™ 2 Quad processor/Intel® Core™ 2 Duo processor/ Intel® Pentium® processor/Intel® Celeron® processor in the LGA775 package . But knowing exact model/make would be better. Q9550 cpu probably.
Google your make/model off your g41 motherboard, the makers will have a section on cpu compatibility. Higher mhz /fsb in the quads /extremes that suit would be best coupled with the highest mhz ram also .
*Note you will also need to update bios that goes with that cpu (if yours isn't that one already) before changing cpu's.