You can not put a PC bulb in a standard fluorescent end cap.
If you are looking for more light with an existing fixture, you can overdrive it and get 40-50% more light out of it.
If you are looking to upgrade, there are plenty of nice retrofit kits out there. AH supply is the best in my view.
If you really want to do it yourself, you can do a PC system by yourself without a lot of hassle. You can simply use standard light bulb sockets and use self ballasted PC bulbs, like you get a Wal-Mart. These are pretty cheap and skip the need for ballasts in your wiring set-up. Additionally, coralite does sell bulbs of this type in 10 and 20 watt sizes. Does not seem like much, but those 10 and 20 watt bulbs are roughly equivalent to 60 and 100 watt bulbs.
There is a fair amount of light lost with these, so a good reflector is important for these. Again, AH Supply has the best. They have Miro 4 reflectors that are as the name implies, very mirror like.
These bulbs are only about six inches long, so you need to plan accordingly, but they work well if you do it right. And they are reasonably priced too.
I am getting a new 120 gallon tank this weekend, and I have planned a ten light system for it using theses that has three separate circuits for dawn/dusk, morning/evening and mid day. Very simple to put together and cheap, cost for the entire set-up is under $150.
Hope this helps you out.
