building a new terminal server HELP

here goes guys
we have a terminal server at work and it needs to be upgraded
currently it runs 2 gig of ram and has 2 hard drives.
what it does is act as a buffer to our network which is a dell network server , this machine is 1 year old and locks up a lot so we need to upgrade.
so what is best? we use microsoft terminal services licence it does xp only and i know we will have to find something software wise that is better .
my question is what would be best for a new server? it handles traffic from 3 cities
and directs it to our main network .
what kind of processor do we need how much ram can we use with windows? wow this is a big order here ,i think i need a link to whats what,
but anyways i am thinking at least 3 hard drives 1 for each city and one larger one for backup.

i will get more details later as i need to get the books from the boss as to what they have and what software we are using
i would like to put this on our dell server as it has 16g of ram and 4 tb of hard drive

any help or points of direction would be appreciated.