I think if depends on what you mean by "use it as a monitor." I assume you will be buying a 27" TV that has an Svideo input--that's really the only way to do what you want. You will then need a video card with Svideo output (many have it).
I've tried this over the years with different computers. Right now I have a PowerMac 7600 and a Ti Powerbook 550, both of which put out Svideo to a TV. I have a 31" Toshiba with a sharp screen. The combination certainly works mechanically but OSX text (or even OS9, it doesn't matter) is barely readable and that is about as good as it gets. Using the internet would, I think, be quite painful. Playing some games with other people (which is probably the best use of the setup) that do not require too fine detail, like Links golf, works ok. Watching DVD's is OK but not as sharp as VHS tapes. if that's what you want, its not really worthwhile.
Since it always seems like such an appealing idea--use you machine as a sort of entertainment center--but is really frustrating, I've asked myself why they put the Svideo output on these machines. I think the answer is for presentations from programs like Powerpoint when only a TV is available.
Maybe my results are less good than others--I'll be interested to see what they say.