OpenGL newbie seeks help!

Hey /prog/, I'm writing a cross-platform OpenGL application which does some off-screen rendering. I've found two ways of doing that - with pbuffers and with FBOs, the latter is preferable. I want old videocards to be supported too.
Now tell me, which technique should I use? Do the older videocards support FBO? Do they support pbuffers?
Thanks.

>>10
Because different graphics adapters and operating systems prefer different endianness.
Also, forgot about the SDL for it is garbage (most notably: SDL_main retardation, very poorly designed video subsystem even in SDL 2). You really should use each platform's preferred windowing toolkit (Xlib, Windows API, Cocoa) and OpenGL.