I dont need to cut out metal, It actually is vented on the back and front and has room for 2 fans (one in back and front) but I dont know if I can tape it on, or glue it (crazy glue is 99c so cheap) I have installed 4 gbs of ram
As you can see I can fit the fans, but no screw holes to put them in
I guess the obvious question is why you want to do this? Low end stuff tends not to need much cooling, and if you have the money to buy fans then you probably have enough money to just buy a better case, a basic one is pretty cheap and often comes with fans fitted.
There is also the potential problem that if you are running a stock dell PSU/motherboard they are likely cut down to essentials, and you might not be able to run fans without adaptors etc.
The pictures aren't very clear at all, but I'm assuming your case is roughly like this http://www.lulusoso.com/upload/20120309/DELL_OptiPlex_3...
with a kind of mesh front.
At a glance it looks like there is plenty of space inside to mount a fan, but both tape and (most) glues have issues with heat/vibration. In layman's terms, warm them up and wobble them around a bit, and they just fall off.
My advice - don't bother.
If you aren't having issues with overheating, then leave it be, it's more hassle for little benefit.
If you are having issues with overheating, try and find the cause. In an older case it's likely to be a build up of dust somewhere.
If you just want a better cooling solution for better components, buy a better case.
Nuts and bolts? At any hdwr store. Or online. Find some in the size that you need to pass thru the holes in the fan housing (usually 6-32 or 8-32) and just the length you need so excess bolt doesn't stick out into the case. You can probably find round head bolts in black to make it look a little better.