What is the smallest hdd i can downgrade to?

Question

Been seduced by the SSD, its not a logical decision, I know. Problem is I cant afford one with a high cap. Take into account I am only using 54GB of my 150GB drive. This is just a short term change(larger drives will come later when prices drop), but I do want it to work well and startup and run quickly. Oh, Intel G2 X25M. I plan to have a bootable drive and TimeMachine partition on the old drive.
If I got an 80GB drive and put the old drive into a firewire case what would be some operational concerns or ways to make the system work better?
I assume SL OX would take up less space, any other ways to manage the overall GB's like 'CleanMyMac'?
I plan to have a bootable drive and a TimeMachine partition on the old drive.
Anyone have a % capacity that they know a drive will still work optimally? Would that also apply to a SSD?
BTW, my iTunes library is 16GB if that may factor into your response.
Apologies to cornelius, changed my mind again I promise to buy something this month one way or another.

Answer 1

ok thats different, you can make your book boot from an external drive, however with what you are wanting especially staying with a ssd you can go as big or small you wont notice the speed difference that is the great thing about ssd however knowing that you want to store files and such i would highly recommend you go with at least the 80gb, keeping in mind that you need your boot files on this. Thats the facts in my opinion though i would stay with a sata drive either a high rpm. SSD are highly overpriced as of now.
Let me know if you need some help understanding SSD.
Another side note when it comes to SSD your not going to notice a huge difference unless the program is a freakin beast that you are trying to load, honestly it only makes up a few seconds here and there. They dont really have a great advantage yet having one is more for bragging rights. Yes i agree its SLIGHTLY faster, but compare Say you have a 640gb sata drive thats more space than you can ever really need on a notebook or the most 256 SSD (another note the bigger the sata drive the faster they read im not sure of the technical terms but i can also explain it if you need me too) but to me id go with the much larger sata drive you will notice a performance increase and battery life as well.