Knowing what file system your hard disc drive - HDD - uses is useful when doing things which require large amounts of disc space.
Capturing a minidv tape of 60 minutes can take up 13gb of space on your hdd, but a fat 32 system will only allow about 19 minutes of capture - 4gb. Whereas NTFS will capture the whole tape in one go.
This page will also add some more information.
To find out what file system you have is quite easy, just open My Computer, click on the drive you wish to check, which will be C: if you only have the one, and then check on the left hand side where it says Details. You may need to click on the down arrows first.