yes you can use it for a Hard disk and CD-Rom at the same time, it's not tooo slow. You can make it quicker by using SmartFileSystem instead of FastFileSystem
I believe it can transfer around 1mb/s,
of course if you wanted more speed the Buddha Flash gives 2 IDE channels and up to 2.7 mb/s, not very expensive either.
I have one and would recommend it.
Robert