anyone in here know how to use power tools?

[Nullcasting]

  i love to get started on projects with no prior knowledge which gets me in lots of trouble.

I've recently aquired a non-functioning Pentium III gateway PC with a case in excellent condition! My plan? Take my current modern Gaming PeeCee and shove it into the old case. Bonus points if i can get the older pentium computer bits working in my modern gaming pc case for shits and giggles. 
course, I didn't, really, er, consider how difficult cutting metal would be until the exact moment the case was in my room - and yes, i think i'm going to have to at least cut a hole in the bottom to allow for airflow, modern pc components get really freakin hot, and there's just not enough holes in the beige beast for air to get in and out.
attached photo of the current disaster that is my room (in the back you can see the water maker i'm using for the Shrimp Tank :V))

so, anyhoo. anyone here have experience modding pc cases? any tips, advice, etc?