Best one I use for AVI (Divx Xvid to MPG4) WMV or reverse is:
Blaze Media Pro
HPQ
Fast
It's not free though..
Try videohelp.com and search for the free ones, I've tried a lot and they crash to many times.
Another one that is good is Mainconcepts from Germany MPEG Encoder for AVI to MPEG1 or MPEG2, you can do batch processing it's easy to do. This would join two AVI to one AVI. Or you can do two MPEG1 to one MPEG2.
D.I.K.O is free but takes time to convert a AVI (D/X) to MPEG2, ISO, Burn to DVD all in one process. It could crash also. The GOLD Version is what they use on the internet to make KVCD versions.
On VOB I use to use TMPEG DVD Author not free though..