optimal hardware for postgres?

I'm just going to buy a new server which will mainly run a
postgreSQL-database and a apache2 with mod_perl and do little more than
deliver loads of index-based select-queries. But it will have to do a
lot of them. And it will be master for a replication to slaves.
As always of course we dont know how many selects we'll have to face.
There will be "many" and the current Athlon1800+ with 1GB Ram is too
slow. (to its excuse : It has to perform loads of other tasks as well)

I was now wondering which hardware would fit this server best. I think
about 2GB RAM, a fast Raid1 and now I'm not sure about the CPU.
I was considering 64-bit AMD : A Athlon 64 FX-51 or a Opteron 2.2GHz.
The hosting system will be a 64-Bit linux.

Does postgres benefit from 64-bit AMD's or would I be better off with a
cheaper AthlonXP or even with a Pentium or a more expensive Xeon?
Or is my question faulty at all, cause CPU is only 20% of the whole system.

Any comments appretiated,
thnx,
peter

--
mag. peter pilsl
goldfisch.at
IT-management
tel +43 699 1 3574035
fae +43 699 4 3574035
pilsl(at)goldfisch(dot)at