if it is a OEM factory tower then chances are you wont have a 6 and 8 pin adapter
or strong enough PSU
there are adapters to change power connectors
what are the rest of your system specs?
as far as bottleneck
I wouldnt be concerned
obviously if you have a custom rig and have the ability to OC the CPU
than that would help
but Pent D ran hot and were not very good overclockers
might be possible to swap in a Core2Duo in that motherboard
since it is usually a LGA775 socket for Pent D
just depends on the chipset used
Pentium Ds are not good overclockers... are you kiding me... this guy knows jack... its easy to take um past 4.3 on air... ofcourse a aftermarket air cooler is needed. I was just messing around with my older Pentium D 945, stock 3.4... running stable at 4.3 36c idle 58c full load Prime95 for 2 hours... this chip can almost hit 5 on air... almost 7 on ln2....
YES, the 8800gt will be bottleneckd by pentium d.I bought a new 8800gt and had pentium d 925,i didnt see any fps boost from 8500gt to 8800gt.when i added a core 2 quad q6600,fps went up by 80 fps in every game,i can play bf3 @ 1400x900 low at 60fps no probs.so yes pentium d will stop ur 8800gt