If indeed you´re going to do lots of rendering, then dual processors is a good setup for you. Rendering is quite CPU-intensive indeed, and takes almost full benefit from multi-CPU setups.
Just a reminder: a 3.06Ghz P4 with HT renders as fast as a dual 2000+ MP. Having that in mind, a top-configured 3.06Ghz is an excellent performer, and might be a good idea if you don´t have the stomach to go with a configuration like this one:
<i>2x Intel Xeon 2.4Ghz 533Mhz FSB HT-enabled: </i>
<b>2x$234=$468</b>
<i>|SuperMicro X5DAE (E7505-based, top-notch):</i>
<b>$430</b>
<i>4x 512MB Corsair DDR266 Registered ECC:</i>
<b>4x$99=$396</b>
<i>ATI Radeon 9700 Pro:</i>
<b>$244</b>
<i>Western Digital 120GB 7200rpm ATA100/2MB cache drive:</i>
<b>$109</b>
So this main core will cost you <b>$1601</b>. You´ll need a respectable case and power supply, as well as a monitor and the usual things like keyboard and mouse, of course, which you´ll probably get with $400 or so (if money is sufficient, you can get a better processor - dual 2.66Ghz will cost you $164 more - or you can get more memory). It takes a lot of guts to want that SuperMicro X5DAE, though, because it supports up to 12GB of ECC RAM (here configured with <i>only</i> 2GB of excellent-quality Corsair, mind you). This mobo packs a <A HREF="http://www.supermicro.com/PRODUCT/MotherBoards/E7505/X5DAE.htm" target="_new">mighty punch</A> (check link to specs). If you want to upgrade later, you can get 2 3.06Ghz Xeons, which are currently state-of-the-art and expensive as hell, or you can get more memory - there are 6 memory sockets on the X5DAE. Tell me what you think! Hope I´ve helped. And if anyone out there wants to flame me or agree with my suggestion, please do!