The PK-232 will be useful for packet mode on VHF. And if it does PACTOR, you can use PACTOR-1 to connect to the WinLink system on HF and send e-mail. However, PACTOR-1 is _slow_.
As the previous post says, most current work with 'digital modes' on HF uses soundcard interfaces. The Donner interface he lists is one way to go. I have an old BuxComm Rascal, which is similar, and has done good work for many years.
Another alternative is the SignaLink USB, which costs more, but has its own soundcard and avoids some of the problems of using a computer's built-in soundcard:http://www.tigertronics.com/
If your computer doesn't have a serial port, or if it runs Windows 7, I suggest the SignaLink USB as the better of the two.
For software, any of the following (in increasing order of complexity) (all free):
. . . Digipan 2.0
. . . flgidi
. . . DM780 (which is a part of "Ham Radio Deluxe")
Digipan works PSK31, and is simple to use and run. The other two are "multi-mode", require more computer horsepower, and are more complicated to use.