I would focus first on your indexes, than have a server admin look at your OS, and if all that doesn't help it might be time for a master/slave configuration.
That's true. Another thing that usually works is to just reduce the quantity of data that's repeadetlyrepeatedly worked with. If you have "old data" and "new data" and 99% of your queries work with new data, just move all the old data to another table - and don't look at it ;)
-> Have a look at partitioning.