Hardware selection

As mentioned previously I have a large text database with upwards of
40GB of data and 8 million tuples.

The time has come to buy some real hardware for it.

Having read around the subject online I see the general idea is to get
as much memory and the fastest I/O possible.

The buget for the server is approx 20K GBP / 30K US$

The data will be stored on an external raid,
SCSI based 2.5TB with IDE disks. Configured as 1 large volume, RAID5. (
We already have this hardware)

Question 1 - whats the best raid configuration for this device?

Onto the server, I have currently priced up the following:
Dell Poweredge 6650
16GB RAM
Quad intel hyperthreaded arch
PERC3Q controller
36GB System HDD
approx 20K UKP

Question 2 - Comments and opinions on this as the postgresql server.
Any comments on better alternatives or modification to this system
would be very helpful!

Question 3 - what would be the best way to distribute tables/swap/
system disk space?

Hope I'm not asking too much...
Thanks !