Yes. A fresh Window 7 installation will fit as it take about 20GB.
But then you have little space for installing program and games (especially games).
So at the end, you may have to disable hibernation, turn off restore point, move pagefile, move default folders to another HDD, etc to save the precious space on the SSD, if you don't or can't use Intel SRT.
I've googled this so many times and cannot end with a concrete answer.
My question is: Can I use a 64GB Crucial M4 SSD as for my OS (Win7 Home 64-bit) ONLY?
I've searched and 50% of the time people say yes and the other 50% people say no.
I don't want to remove any OS files or anything of the sort. I just want a yes or no answer.
Can I use a 64GB SSD as a boot drive only?
Sure can, check my configuration. Have no idea why anyone would tell you different, its actually the preferred way to set up an enthusiast's build at this point in drive technology. Put your OS and your antivirus software on it, and enjoy a super snappy rig that is a pure pleasure to use.