Just wanted to say thanks to everyone for taking the time to reply top this thread.
As stated above, my dell power supply unit did not come with any molex connector (if that's how you spell it) and as im planning on getting a few more things for it i decided to get a 500w power supply which came with the 6pin connector for the 8600gts card. It worked fine after installing and you can fit any standard psu in the dell dimension e520 with the psu model i had (see above) everything now working great and vista score jumped from 3 to 5 and games such as age of empires 3 and command and conquer play at full graphics setting which im really happy with.
Hope this thread helps other dell users who feel a bit stuck with the factory spec and layout inside
Merry crimbo everyone