Are the new 2.4.x kernel backwards compatible with the older 2.2.x kernels?

Ever since I have upgraded, many of my aplications just stopped working. Some were fixed with upgrades, others I am just leaving alone. I think it would be an issue with the kernel, but it could possibly be the applications. I'm looking for some guidance as to what it might be... (Or if anyone knows about the two types of kernels.)

BTW, obviously newer=better (most of the time). I am looking for some opinions. I was using the 2.2.14-5.0 kernel. Would my transition been easier if I upgraded to the 2.2.18-XX kernels or did I make the right move by using the 2.4.2 kernel?

I really like the 2.4.x kernels. That being said they are not 100% backwards compatible. Some apps will have trouble (real server comes to mind). Did you install devfs? This will probably cause problems with some programs. If you are having problems with a lot of programs something else is probably amiss.