You need at least a gig of memory. I would fill it up. 1 gig sticks are only $130 and 512's are almost free.
Dual CPU is fine and is better than a single slightly faster single CPU. Remember 2 cpus can do 2 tasks at once. Try that on your single board.
I wouldn't bother with RAID 1. If you are going to buy the hardware get a card that supports RAID 10 (or 0+1). Of course you need double the drives for that but in reality I am getting rid of my RAID and sticking (in Oracles case) logs and etc on 3 or more different drives. Add swap space to all of them and you are flying.
If this is a life or death, lose your job if you have any downtime then by all means use RAID. If not, drives are so reliable today that you will, most likely, outgrow your drive before it fails.
Having things on 2 or more physical drives adds reliability (and of course cuts your MTBF, but I am willing to take that risk) and lets your controller work much better.
Of course, this is my opinion and I am sure someone will tell me I am full of %^&* but ....
