Long title, short story: I found a very comftable way of recording Let's Play audio and video that requires minimal effort and synching. The idea is to choose the same record hotkey for Fraps and Teamspeak, so that both files will be in sync when combining. Using Virtual Dub to extract the ingame sound, Audacity to adjust both channels and then mixing it back in with Virtual Dub works really fine I have to say. I'm been playing with different way of recording for a while now and this seems to best one so far. Too bad that I started recording stuff before I found it out, so I'll need to post-edit my old videos... However, you can even properly split the rendered using the "Save as Segmented AVI" menu option in Virtual Dub 1.9.11. For 60 fps video, 54000 frames is the limit for 15 minutes recording, so just remove a few and you should meet Youtube's length limitations (yep, I'm not interested in giving Google my phone number just for longer videos).
So yeah, recording setup is ready to go and I only need to cut the old videos. I mean I really just have line them up and shift the audio a bit. Shouldn't hurt I guess?