You will be surprised at what is running in the background on a PC. I use a utility called EndItAll to make sure I have a clean PC for editing. Do a search for this free download.
Defrag your hard disk. This can make the PC work harder than it really needs to if bad fragmented. Also make sure you have plenty of free space on the drive. DV footage takes 1Gb of space for 4 minutes of captured footage, plus space for editing
A second disk is also a good option for capturing the footage. If the drive is accessing programmes while copying the footage then it can drop frames as it is working too hard.
Mark.