I was having the same issue with some theme's I was trying.  Had to log in as admin (which didn't have any specific theme set so used the windows default), unpatch the files and reboot before I could log back in again.  I don't have any specifics of what I was doing with my theme.  But checking the event viewer showed that something was crashing during login which is why it wouldn't log me in and kicked me back to the login page.  I've been using ~psycoB's StyleSelector since then as that applies the theme after login.  That and I haven't been doing much with my themes lately.  But I've also been having issues with StyleSelector on my work PC where I was getting kicked out of my remote desktop when it tried logging in.  Had all sorts of weird things in my event viewer from that.  So I've stopped using StyleSelector at work.  Hopefully the AveStyler I just bought will work better.

Just tried the fix from this thread about saving from Paint.NET as 32-bit png (not auto-detect which is what it uses by default) and my crashing appears to have gone away.  Wu-hoo!

Oh, just tried it on a third Vista PC.  This is my wife's laptop with Vista Home Premium 32bit with SP1.  Doesn't crash when I do the same things that causes the other two systems to crash.  Only thing different other than home vs business and ultimate is that this one was pre SP1 when I got it and has since been upgraded to SP1.  Although I also haven't had the same issues I've noticed on the business one with "unsigned drivers".  I can and have installed RMClock, CrystalCPUID and Ultra Defrag on this laptop without issue.  As I've been trying these on my vista business PC, I'm running into all sorts of headaches with signed drivers that apparently was added with SP1.  I remember having issues with SP1 on this laptop at first.  i think I uninstalled it once or twice.  Maybe something went funky where it's only partly installed or it just thinks it's installed when it isn't.  Hmmm.

Were you suggesting that I shouldn't have SP1 installed?

Nope.  I've had the same issue on two different PCs.  One with Vista Buisness x64 and one with Vista Ultimate x86.  Both with SP1 and all patches applied.

I just started playing around with VSB and have had a lot of crashes.  I can consistently cause it to crash by doing this...

1) Start a new style
2) Go to Windows and Caption Buttons->Basic->FrameLeft
3) Edit the image. (Using Paint.NET)  If I don't make any changes it doesn't crash.
4) Close my image editor to return to VSB
5) crash!

This has been happening with a lot of images that I try to update.  At least in the window frame area.  Start button and taskband toolbar buttons I was able to update without any problems.