This is often an issue. You are probably losing (dropping) some video frames at the start. One way that might get round this is to record at a lower video quality i.e. a lot less work for your PC, and you might not drop the video frames.
Don’t forget the video is not as high a quality to start with as a DVD - you will not improve the picture by reording at highest video setting. Try recording as VCD quality which is close to VHS quality say.
Another way round that often gets round this it is to output from the video in RF mode (i.e. via the ariel lead rather than via scart) and tune the PC TV tuner to the Video RF out channel. This often works as the audio and video signal are combined whereas when you separate then using audio in/video in channels, the PC does not always align them well. You may lose some quality though compared with scart video. Again as above, you probably do not need to select full DVD video quality.
There are also software packages which will allow you to realign the audio/video e.g. virtualdub mpeg2 (freeware), but it is normally a fairly laborious trail and error procedure to do this.
To be honest, given now a cheap stand-alone DVD recorders is Â£80 or less, it is more hassle to use a PC in my opinion. It will cost you almost as much to buy a new card /software (without a guarantee of success).
The downside of of a standalone is that it will not normally copy macrovision protected VHS tapes (there are ways around this search for macrovision).
There are also now combi dvd-vhs recorders (i.e. both recorders) which even avoids using connection cables.