Various Windows XP issues I've encountered noted here in case these notes help anyone else overcome similar problems...
Outlook Express 6 hangs with an hourglass in various situations. Firstly, its "Switch Identities" feature is known to have problems under XP - this is well documented on the net. With the latest updates applied it seems to work tolerably well if not 100% reliably. Secondly, I found it would sometimes hang when trying to view a particular email folder, or sometimes would get into a state where it would hang on startup. Initially some of the email folders appeared to have been corrupted (fixed by replacing the .dbx files with known-good backups). But later it seemed that the problem might be related to AVG 6 free edition anti-virus software which was also installed. In particular, unchecking AVG's "Use Outlook Express 5 plugin" option seems to have solved the problem.
Explorer.exe kept crashing when trying to open images (errors such as Explorer.exe Application error. The instruction at 0x77f580db referenced memory at 0x002e0041. The memory could not be written. Click on OK to terminate the program). Other symptoms are it taking an age to display icons for image files. The culprit in my case was Photoshop 7, which attempts to create thumbnails whenever a folder is viewed in explorer. To disable this, right-click on any image file in explorer, go to Properties, go to the "Photoshop Plugin" tab and uncheck "Generate thumbnails" (possibly you have to do this for each file type - but not for each individual file). Another option is to rename "psicon.dll" and reboot, which disables thumbnail generation by photoshop.
This problem also discussed here.