not directly..... you can get a general feel by going into your suggestions after you have rated some shows... long list=more space
They did this becuase of the way it dynamicly stores things... such as one show being set to save for at least 7 days and another season pass set to only keep a few episodes.... it takes a bit but you will probably like it better.
Also, all programming it records is recorded using a Variable Bit Rate.
As such, the exact amount of disk space to programming time is always variable.
TiVo could, if they wanted, try to estimate, but then they'd have to deal with complaints about it being inaccurate. So they just leave it out.
Shadow is right, though. Once you get used to it -- let TiVo manage the space. It's easier to not have to worry about it.