What hardware should I buy to setup  VM Ware?

Consider we have a sizeable data center with over 100 UNIX host and
1000 + Windows servers.  Assume we will deploy numerous TEST and PROD
servers into this new VM Ware environment.   And that we will spring
for VM Ware's top of the line ESX and related tools like VM Virtual
Center and VM Motion and other tools VM Tools for High Availablity.

Whose hardware?  And what configuration?   For example we have some
IMB xseries 346 and 445 boxes.  We also have some HP Proliant series
that runs Windows.  Obviously there are many options.

I feel the mgmt assumption here is that we would buy maybe 3-4
sizeable boxes (like IBM xseries 345) with say, 8 CPUs and 32 GBs of
Memory.  But, a number of smaller boxes would also seem like a good
idea.    Manage distributed servers as a single pool of resources.

Ultimately I need to chose some hardware and obtain some quotes.