Something on my Windows 2000 machine seems to have changed recently that caused this behaviour: whenever I start Outlook Express, the message header listing and the preview pane take forever to display (up to 30 seconds compared the original 2 seconds). I thought it was because I had moved my mail folder to a secondary hard drive that was going into sleep mode, but that was not the case. I also found something on MS's website about imagehlp.dll (or something like that) being an incorrect version. I messed around with the two versions I had available and that did not have any effect.
Any ideas? Outlook Express is the only program that exhibits this strange and rather annoying behaviour.