No- SATA III drives automatically downshift to work within the bounds of SATA II drives.
The one thing you need to know is that the T61 has a certain limitation in that it only actually performs at an SATA I level (that's 150 MB/s.)
There exists a workaround BIOS that will enable the full 300 MB/s (it also does other stuff)- just search for 'T61 SATA 2' on Google and you should find it no problem, though beware that it will void any remaining warranties on your machine, and is risky to install (just like any other BIOS upgrade).
So if you use this mod, you'll want something with a Sandforce controller for maximum all-around performance.
Crucial and Intel drives are good too, though the RealSSD C300 is limited somewhat by the fact that you are hooking it to an SATA II interface, and the Intel drive has better boot performance than SandForce drives but lags in pretty much everything else.
Even if you don't perform the mod, the above still holds true.
Be aware that an SSD that's over 160 GB will consume over 350 dollars of your cash.
Also, beware of OCZ. They have an 'issue' with a certain kind of flash (their new drives, the ones whose part number ends in E, are slower and smaller than ones that don't end in E: and even if you buy a "non E model" there are no guarantees that you'll not recieve a handicapped one).
They are a good bit cheaper when it comes to large capacities, though- so you need to decide: cheap or fast.
Also, you should still take a look at the dimensions when you've found a drive you want, though I believe they all come in 9.5 mm sizes. Just don't pick a 3.5" drive.
