I don't know if I'm just blind or if it's totally hidden, but I can't seem to find anywhere how much hard disk space I have available. I think I'm running low on memory (ROM), but I don't know how to check
You can show info on the HD but I think they need to be on the desktop to show this info (I'm away form my comp so I'm not sure but I know there was something messed up about this.) Or you can go into the terminal and type df. If you find my post about file utils under Unix discussion you can get a better version of df and use the -h option to make it more readable. It also give you a general amount of info in the status bar if you click on a disk in a Finder window.
In the finder, under view, make sure "show status bar" is enabled. with that, just open up a window in the hard drive you want to check on, and it'll be listed there, right below the toolbar.