Laptop restricted to specific SSD size

I have a laptop (Core2Duo) at this stage it is four years old, I'd like to squeeze another two more years out of it, maybe 2.5. I was planning on doing the last upgrade I could for this laptop which is the HDD, currently has a 5400 (320 GB) it's a larger HDD, but slow. The manual states that the max size I can put in this Laptop is a 128 Gig SSD, the problem is cramming the Windows partition into a 128 Gig SSD. Any reason I can't put in a 240 gig ?

Don't ask about accessing the BIOS, you can't, I've researched and the only thing I can change is the boot order, if you wanted to boot from a DVD instead of a HDD. It is a good laptop, I still love it, just heavy but I can throw quite a bit at it, compared to the laptops sold today which some seem to be on an equal plane to mine.

Hiyya Jerome why only 120Gb they are all the same size - physically and well it doesn't make any sense that after using a 320GB for some time why would a 240GB make any difference.

Suppose there is one one to find out mate and that is just stick one in.

Now if you only use the machine for day to day stuff both my laptops have 120GB in them and I just don't run out of space at all. Currently my best one a Toshiba L550 on it the OS and heap of other stuff like Essentials CC, MBAM,Kaspersky, Office etc etc only uses up about a quarter of the drive if that.

Anyway size (GB) wouldn't stop me from throwing one in and I would go the Plextor it has a 256GB and reasonably priced - out here that is, and it is not a Sandforce one either. .