Dual channel isn't going to make or break his ability to run AH.
Trust me I've done it all over the years in regards to AH. Dual channel, non dual channel, single stick, slow CPU, slow vid card, and upgraded to many different stages of CPU, GPU, and RAM.
His ram is perfectly fine. Going from single channel 1.5 GB to dual channel 2 GB (edit: and changing nothing else along with it) would be a fart in the wind as far as AH is concerned.
P.S. He said his current CPU already supports HT. I had one that did as well, really not a fast CPU. the 3 GHZ plus range of P4 chips are okay for AH, but even the lowest end Conroe chip will smoke a 2.4GHz Pentium4.