you should find that your computer will boot up faster and your programs will start-up quicker.
in simple terms, this is because during boot and application startup, windows needs to load lots of small files from the drive into memory. with an ssd, these files are accessed and loaded much much quicker than with an old-fashioned spinning hard-drive.
it won't 'speed up your whole computer' in the sense that games (for example) won't run
any faster, but they will load
laster - so rather than waiting say ten seconds for a game or program to become usable, it'll be only a couple of seconds instead.
i don't think i've heard of anyone regretting buying an ssd. speaking for myself, i won't go back to a hard-drive for windows, although i have kept my old hdd for mass storage of things like music and movies, where speed isn't essential - i don't need to watch my films at high speed.