OK to try and prevent any more arguments - there is no 'you must do' but several suggestions to help reduce/eliminate dropped frames. Lets keep the posts helpful and see if we can help the OP
Right, I suggest you track down a copy of the free & helpfull program called EndItAll2 from the internet to stop all unwanted background programs (PM me if you want me to e-mail you a copy - but be patient as I am on nightshifts all weekend).
Defragment your HDD as this may well help. Also you should have plenty of sapare space as .AVI files eat up space at approx 13Gb per hour captured. As space runs low the performance of the HDD drops. I always suggest that to capture 1 hour of footage you should have around 25Gb of space. Also make sure that DMA is enabled for the HDD as this often improves performance.
There a loads of things to try, but start with what has already been suggested to see if that helps. A search of this forum for 'dropped frames' etc should bring up plenty of reading to keep you buisy for a few hours.
Good luck and let us know how you get on,
Mark.