CJ, sounds like a video head problem - the pixelation is due to the digital stream being broken.
I would find a reputable shop and have the unit professionally cleaned. Every one is quite correct - head cleaning tapes are bad news - with the rotation @ about 1800rpm, they are abrasive and the wet ones just throw the gunk around in there.
If your unit has many hours on it - it may need service, possibly a new head or perhaps it has an electronic problem (servo - head amp) = $$$.
New may be a better option if this unit is older than 5 years. (and was less than say 500GBP)
Besides a trip to the shop, the safest and most consumer friendly way to clean your heads is to buy a
brand new high quality tape and run it on record for a 1/2 hour or so then try scanning a bit.
1. I can't find a video file joiner which works - the curiously named 'Wiagra' doesn't work (sort of like eleven of the dozen oysters!! )
Let me get back to you on this one - however give windows Movie Maker a try - even does MPEG4 compression.
http://www.microsoft.com/moviemaker will give you a redirect to resources on it. It's erm, free.