The 33 is measured in mhz and doesn't have anything to do with your ATA specs. You can have a PCI bus @ 33mhz and still use ATA133 or whatever. Realize though, that the supposed 100mb/s bandwidth is just theoretical and it is unlikely that you will ever see speeds like that. With my fsb and the ram I am using matched @ 390mhz, they (manufacturers) give me a theoretical memory bandwidth of 3200mb/s, but I rarely see above 2800. You'll likely see 30-50mb/s or so for your hd.
As for your next question, it all depends on what your going to spend, and what you need from your computer. Almost all hardware can be made to work with some effort, but it is always nice for it to work easily