i just installed the wd 300 gig 10k rpm hd. my question is, would there be any performance decrease by haveing too much space left over? or should I partition say the c drive only for the space necessary for window?thanksps this turned out to be a fantastic upgrade!

Multiple partitions on hard drives are pointless in the modern era of computing. Choose the maximum allowable partition size.

i just installed the wd 300 gig 10k rpm hd. my question is, would there be any performance decrease by haveing too much space left over? or should I partition say the c drive only for the space necessary for window?thanksps this turned out to be a fantastic upgrade!

Actually the opposite. Theoretically, the less portion of space available out of the total space will decrease performance, with a measurable decrease starting sometime after 50%. Also, you should never partition a drive if using it for anything but storage, as it can also possibly slow down read/write and seek times.