After Effects Render SLOW - Slower than my old PC

I am using a new 1 month old 20" iMac, 2.0Ghz with 4gb DDR2 RAM, running OS X Leopard. Adobe After Effects CS3 is rendering really slow, and I mean like the same as my PC. Also the same with Premiere Pro, it renders really slow and I have tried different formats too, in premiere pro it took 2 hours to render a 5 minute video (saved to .mp4 640x480 pixels, end size was 20mb). This is wayyy to slow.

I compared my Mac with my old PC running Windows XP, it is pentium 4, 3.2Ghz with Hyper threading technonlogy and 1.5 GB DDR Ram. I tested rendering andrew kramers 3d room tutorial, I downloaded the project file. I only chose to render some of it and the old PC was FASTER than the Mac by around 15-20%. BUT, the mac was ONLY using 6% of the 3gb (it only recognises 3 gig not 4 but I dont mind that too much) and the PC was using 60-70% of the 1.5GB (thats using more RAM than the mac) So why can't I get the Mac to use more RAM when rendering, and why is it slower??? It is faster at EVERYTHING else, well the ram preview is about the same.

How can I get my mac to use more of the RAM and why is it rendering and previewing the same if not SLOWER than my 5 year old PC?
Any help would be awesome, thanks

- Dillon

If your Mac is only recognising 3GB, are you sure it's the new model?

The old Core Duo iMacs (white) could only access 3GB, but if the memory isn't balanced (i.e. 2x 1GB sticks) you couldn't get some dual access speed benefit thingy...

Also make sure you have the latest updates for everything... Premiere Pro was only scheduled to be fully Leopard compatible in Jan 08 I think.

Yes I have the new model, I got it a month ago and its not the white one. I've been on the site and the max is 4gb and the Operating System says it has 4gb just not after effects (its the silver mac by the way).

I got latest updates and everything, thanks for your help though I hope someone else has more suggestions.
- Dillon