I would recommend going to www.monarchcomputer.com
or a similar reseller which will let you customise it
for a little information about Athlon 64's against Pentium 4's:
AMD has created the P-rating (or Performance Rating) which measures their performance against other CPU's. they were originally designed to compare with their old Thunderbird processors, but also compare well against Pentium 4 processors.
basically, a 3700+ CPU will roughly compare with a Pentium 4 at 3700MHZ
it has to do with the actual architecture of the CPU. the Athlon CPU's will process instructions in a fewer amount of clock cycles than Pentium 4's
also, DDR2 does not give Intel CPU's much of an advantage in memory bandwith.
to communicate with the memory, the Pentium 4 has to talk to a memory controller on the motherboard which then talks to RAM
but the Athlon 64 has its own memory controller on chip, so it can communicate to memory a lot faster.
although DDR2 will give the Pentium 4 a slight edge, only because DDR2 is faster.
But after about Q2 this year, Athlon 64's will also support DDR2. this, coupled with their onboard memory controller will give the Athlon 64's a big advantage.
Hyperthreading (HT) is a technology Pentium 4's use. it basically tricks the computer into thinking there are 2 CPU's, so it will send 2 instructions at once.
Intel has now made dual core Pentium 4's (called Pentium D's) which render Hyperthreading obsolete.
however, AMD also released dual core CPU's after that. they released them later on, because they spent more time on them, and they outdo the Pentium D's in just about everything, including price.
if you use CPU-intensive programs, it might be worthwhile to get a dual core CPU.
there's the Athlon 64 X2 3800+ for starters