My pc doesn't have enough ram to run steam so i want to know if theres any way to use the hammer on mac.

Not really. Hammer has a lot of windows dependancies and is thus incompatible with Mac.

I just recently setup up a separate partition on my hard drive running Windows 7. You Mac should have a program called BootCamp which will take you through the process. This allowed me to install Portal 2 and Hammer over on the Windows side. Working great so far. You do need to have a full version of Windows you can install though.

if your computer has not enough ram to run steam I'm afraid that hammer won't work...
Hammer often uses about 1 gb of ram!