After disabling an entry in the hosts file to allow that domain to be accessed, I've found it necessary to quit and restart both Internet Explorer and Outlook Express before I am able to access the previously blacklisted site. Is there any way to force these apps to reread the hosts file other than to quit and restart them?

Maybe Flush DNS cache will help?

I have that in the right click menu but you must enable it in Tools Options General

By the way, I use McAfee SiteAdvisor on my XP Pro system and SiteHound on my XP Home system to warn me about nefarious sites:
http://www.siteadvisor.com
http://www.firetrust.com/en/products/sitehound

Thanks YoKenny.

I tried flushing the DNS cache, but I still had to quit and restart IE an OE.

Thanks for the links.

What OS are you using?

XP Pro SP2 with all subsequent updates.

Most web browsers have their own DNS cache and that's also the case with IE (I don't know if IE6 in Windows XP has its own DNS cache, but IE7 has). This is the only information I found on how to tweak IE's DNS cache, but it doesn't apply to IE7 nor to Windows XP and Vista: http://support.microsoft.com/default.aspx?kbid=263558

You could try with DNS client service enabled (this one can be cleared), but it might degrade the system's responsiveness.

If you have a large HOSTS file then performance will be impacted as the HOSTS file has to be loaded into the DNS Client Service memory.

If I modify the HOSTS file I always end IE and OE to be sure that they are using the updated version.