There are some 3rd party components (no freeware of course!) or you can use API calls in CPP style or even better write a DLL in CPP and call it from VB.
IMHO the simplest way is to use OCX named "Microsoft comm control 6.0" (part of vb6) which was created to let VB communicate with modems, but works fine with any serial line connected device. Plus you can use samples written by MSC documentation team e.g.:
http://support.microsoft.com/kb/194922
