Hey there, as chrism01 said above, why are you using a beta? here's a warning, your problem may be because you're using a beta version, you shouldn't use a beta release unless you're prepared if things break, I recommend you get the 9.04 stable download as it sounds like you're not too experienced with linux.
Also, how much free space do you have, you might not have enough
Dual-boot with WHAT? What two OS'es are you dual-booting?
From his user agent icon, I guess he's trying to dual-boot with XP and/or "ultimate linux 2.2"