Just a note for those of you having trouble with Avantgo.
I was having all kinds of trouble just like you. I tried copying the .mui file manually and also tried Tweaks to force it, but each time the text would pile up ontop of itself and I couldn't get it to work at all.
However, I ran across some info that told me I needed the tgetfile and have it in my /Windows folder.
Now, I Avantgo works great in VGA. I have 2003SE, so I can't guarantee that it will work with WM5, but it may be worth a try for you that are having trouble like I was.
Note: I got my copy of the tgetfile from Tillanosoft at thist address:
http://www.tillanosoft.com/ce/tgetfile.html
Hope this helps someone.