You can connect any MIDI keyboard to a PC ( including the ones you mentioned ) and just requires the MIDI interface plus software. Cakewalk makes a range of MIDI/digital audio sequencers. The home version of Sonar
http://www.zzounds.com/item--CAKHS should be fine and includes a couple of soft synths plus you can add more DXi and VSTi synths as required. M-Audio are well known for their USB MIDI interfaces eg.
http://www.zzounds.com/item--MDOUNO Hope that helps to answer your questions.
[This message has been edited by Nigel (edited 12-30-2006).]