Well, actually, using, or at the least making an emulator is pretty much gray legally I think. I never could force myself to read the WHOLE Lincese agreement of the PS, but it was very unforgiving for any kind of third party software. I don't remember if it mentioned emulating specifically, but I doubt they would happen to like the idea.
Before even starting, you should check wether the game would run at all! The PCSX2 website has a very useful compatibility list. Most games are playable by now, but best to be sure.
As for the emulation: Well it IS very uneffective, so you'll need a far more powerful machine for playing a graphically demanding game (don't be fooled though, graphically demanding games mostly use a hellish amount of processing time, a good graphic card is only needed if you want to play on increased resolution, and from what I've seen, the important part is the video memory). For example FFXII, Personas, etc. Old games, on the other hand might work with slower PCs. This is not neccessarily true though, so don't expect anything. It depends on how unorthodox the game's programming is (for example, it took the developers a very long time to get Tri-Ace games running, and Star Ocean 3 is kind of slow and you never know when it will just stop,) or so I've heard.
Also, don't forget to update the plugins for the emulator, or if the game is completely unplayable still, or shows some very strange graphical bug, then try to search around for compatibility issues with specific settings and plugins. Also, you can play around with hacks, and there are some (though less and less as the development proceeds) game specific hacks. If the game is not very unstable, glitchy, just slow as hell, then be sure to use speed hacks. They are a bit risky, but not that much as to avoid using them. If the game runs fine without them, then no need, but that is highly unlikely at the moment.
I say, if you have a PS2 that isn't on the verge of death, use it instead for now. PCSX2 works fine, but you'll have a lot of work with it and that doesn't guarantee that you will get your game working. I was not so fortunate, so I use it nowdays instead of poor PS2.
Ah, and you can use the plugin called "lilypad" and you can use a controller. If you have a dualshock 3 controller and say a 64 bit windows, then use motioninjoy (google).