.avi Files not Being Played Properly.

[SkyFrontier]

I'm not into watching video in computers, so I can't tell the frequency this is prone to occur nor since when.
Fact is that I'm having to open .avi files via WE if I want to see them without any hitches.
Testing:
VLC player 1.1.0, XP sp3, no codecs installed that I'm aware of (except by any OS defaults; this is a pretty clean install).
avi1.avi > opening it via XY leads the video being opened but distorted (some diagonal lines crossing the view port); sound plays ok. Closing it and opening the same file via Windows Explorer (WE) shows no problem. If then I close/open the same file again from XY interface, all goes fine.
avi2.avi > same stuff.
-avi1.avi again, out of curiosity > I have to repeat previous steps (open the file from WE, close it THEN open it via XY) if I want to run an .avi from XY.

Workaround: open .avi from WE!

Curious observation: I've installed some .net framework packs (2.0 and 4.0) to test some apps (Tabbles and FinePrint 6.12/6.13 - which does not require .net, but are in the test menu today) and that strangely solved the problem, as far as I can see.

Can someone please confirm? Thanks.