external hard drive and time machine!

dear friends,
i am looking to buy an external HDD to use with time machine on my mac. The thing is I also have a Macbook pro with Tiger on it and an Airport Extreme. If i connect the hard drive to the Airport, will the Macbook see it and be able to use it or just my iMac with Leopard? The iMac has a 250GB internal drive and the Macbook pro has a 120 GB internal hardrive. should i be looking at the 500GB or 1TB external drive if I wanna use these two computers with it? Also do i need Firewire or just USB considering the USB only version of the external drive are cheaper and the Airport extreme doesn't have a Firewire port. This drive will primarily always be connected to the Airport so i don't know if I need Firewire.I searched on the internet and couldn't find an answer to my question.

these are the two drives im looking at:

http://www.tigerdirect.com/applicat...ODE=NEXTAG&cm_mmc_o=2mHCjCWw0fzTCjCVqHCjCdwwp

and
http://www.amazon.com/LaCie-Externa...2?ie=UTF8&s=electronics&qid=1232406015&sr=8-2

Thank you very much,
Jay

so the 1TB drive is the best option? Also, will my notebook be able to access my time machine iMac back ups or not or vice-versa? and the notebook can't use the drive if I don't partition it?

Artful Dodger said:

Is this because you just want to access some files to off load to each? The way it was explained to me at the Apple Store was once the external drive is setup with Time Machine and backed up, you could use it as you normally would and thus if the need be to place files from another Mac on it you could and your notebook could read those files (bearing it's an iBook or MB to iMac). I had no need to ask about windows to Mac if that is your question. Hope that answers your question

Click to expand...

what i mean is if i use the external Hdd with time machine to back up my iMac. could my macbook pro also access the iMac back ups. Also, say i back up my iMac to the external hdd. could i also back up/store files from my macbook to the same external hdd when there is already an iMac time machine back up on it or would i need to partition it?