Installing windows xp to a computer with only the bios on the pc

Hello i have question that is puzzling me, i need to install windows xp on a pc i got for free from work which works great its a dell optiplex gx270, the only problem is since it was a work station pc only has a 40 gig hard drive but a 2.80 pentium 4 processor. it did have a bios password but i already bypassed that and disabled the password i have an external cd rom drive i can use if i need to make a boot cd but i should warn you all i normally am a mac person i prefer it over pc's but this is just so that i can upgrade my blackberry software and a convert wmv files i couldn't convert without paying for it on mac. i haven't tried networking it to my mac yet which i could easily do but if need be i also have two external hard drives too anyhow if you have any thoughts it would be greatly appreciated.