Raid set-up Where are my 80 gigs?

I just installed a raid array o striping,
Two wd 40 gig ulta ata 7200 rpm drives.
Problem / the computer see’s 40 gig?
I have a htp raid program that see’s the two hdds as master primary and master secondary.
This is a abit th7-raid board P-4 1.5 gig 128 rdram pc-800 non ecc.Also can I add slaves to these with out fdisking the whole array? I think not on that one?