Recently I purchased a DreamHost account, seems to go pretty except for a few small things.
Bottom of this article is my full PHP5+IMP tar ball ready for download so you can get going with the good stuff.

Annoyances with dreamhost..
• Dreamhosts's default PHP5 does not have IMAP extention installed
• You gotta pay extra per month for SSL portforwarding to your IP address (what a jib!)
• It's a cheap hosting environment so no they dont let you just edit /etc/php.ini and add lib_imap.so, as theres lots of nasty php scripts out there that will do all sorts of terrible things to their PHP 5 / IMAP servers. - so you gotta compile your own PHP..

Dreamhost have their own webmail, so this isnt about installing their existing webmail on dreamhost
Now not being scared of a bit of dirty work i googled for dreamhost compile php cgi-bin and followed the following http://blog.dreamhosters.com/kbase/index.cgi?area=2538
One thing they dont tell you, is to 'strip' your compiled PHP5 binary, it will reduce it from 60mb (yes 60!) to 6
 
Before..

-rwxr-xr-x  1 dgtlmoon pg923820 20497678 2006-09-29 07:27 
php.cgi

[willie]$ strip php.cgi

After..

[willie]$ ls -al
-rwxr-xr-x  1 dgtlmoon pg923820 6278448 2006-10-03 07:27 php.cgi

Here is the download link for PHP5 with IMAP compiled on a dreamhost server, ready to install
php5-imap-dreamhost.tgz

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