The TS-450S will work fine under computer control, but you need an RS-232 (+ and - 12V) to TTL (0-5V)level converter, such as the Kenwood IF-232C, to make it work with your computer. The feature set that is exposed to teh software may not be as great as is offerered on some newer radios, and I think the data rate is only 4800, but it's still fun to use software like Ham Radio Deluxe with the rig.
If you are inclined toward building electronic stuff, you may want to look at the Maxim MAX232 chip as to buld your own level converter. Otherwise, you can build one using the old standby 1488 and 1489 level converters. I just looked on the web and searched for "1488 level converter" and found the following page: http://www.surducan.netfirms.com/RS232.html
for an example.