The "squarish" title bar can occur when an application is hanging; basically, the XP theme engine stalls and the window chrome from the basic UI shows through.

What might help is to open the task manager, select the hanging application in the applications tab, right click and select "go to process." If this ends up highlighting csrss.exe, your problem is most likely a GDI leak somewhere... possibly related to a module, or to a completely different program. Do not kill the csrss process, tho.

If this is what ends up happening, keep an eye on what programs you've had running for any length of time. You may also find it useful to download a copy of GDI Resource Saver and see if that uncovers any problems:

http://gdisave.sourceforge.net/