O'C Limiting Factor

when it comes to overclocking, is the motherboard's FSB the highest you can go as far as an FSB overclocking on the cpu? and when manufacturers come out with slight variations on a same class cpu of the same FSB speed and cache, is their only difference essentially the manufacturer increasing the multiplier? and bwt the majority of overclocking is done through the bios right? cuz i will be attempting this for the first time as soon as my order comes in this week. i think the default multiplier for my 2600+is 11.5, so i will first try to get the FSB up to 200, to sync wit my ram.

Most overclocking is done by increasing the FSB speed in the bios. However, with amd mobos there may be jumpers as well/instead. In bios, you are limited to what the manufacturer has supported, but that is usually much more than you could ever reach, if you have a board from a good OC'ing manufacturer.
Changing multipliers can also be used to OC, but most chips have their multipliers locked. You can sometimes unlock them, but not always.
Not sure what you meant by "class", but for example on Barton 333fsb amd's, the difference between a 2600+ and 2800+ is increased clock speed by increasing the multiplier.
The limiting factor is usually heat.
HTH

so if you could get rid of all heat generated then your cpu could really go as high you want, without shortening its life? i know this is next to impossible for most people but i was just wondering.

Well, not quite "as high as you want", and it would adversely affect the life of the cpu, but using phase change cooling, you can get very high OC's.
Tomshardware.com used liquid nitrogen to OC a P4 over 5ghz.

In my limited experience, the temperature to CPU speed curve is very non linear. You can bump up the speed with only marginal temerature increases until, BOOM, a minor speed increase crashes the CPU. I guess it can only take so much and then the temp spikes up.

Well, heat isn't the only thing that makes an OC unstable. http://www.hardwareanalysis.com/content/article/1482/ gives a good explaination of what goes on with an OC, and why you need to increase the Vcore to stabilize a higher OC.