Kernel Support for Dual Core x86-64?

Hi all-

My company is looking to build a cluster of Linux machines to run an
in-house compute-intensive application.  We're strongly considering
dual-processor, dual-core x86-64 systems for cost reasons (shared
hardware, less rack space).  I have a few questions, and despite
extensive googling, haven't been able to find satisfactory answers.

1. Can a dual core chip run two os-level *processes* simultaneously or
only two threads from the same process?  Our processes (written in
Python, with parts in C) are completely independent of each other.

2. What sort of speed up relative to a dual processor, single core
system could I expect to gain?  I realize this is highly application
dependent and I'm not looking for any hard figures.  I just want to get
a rough idea to see if the additional cost is worth it.

3. Any suggestions on compiler version?  We're currently using GCC-3.3.6
on our 32 bit boxes.

Thanks in advance!

-- 
Peter Fein                 [email protected]                 773-575-0694

Basically, if you're not a utopianist, you're a schmuck. -J. Feldman