allocation of harddisk

I have a new pc with 2x250GB harddisks WD2500JD .
after install xp it just shows app 120GB
1: How shall I now reach the disks, and allocate so much as possible of the 250GB on both disks.
In win98 times I had no problems as I used a Start up disk, but here it is so large disks, that a start98 disk do not help me any more, as to 64GB or so … HELP