you can do that. this is a code that i'm using in my flash skin to acheive this:
its a little different in vb6 but it'll still work, basically u create a vb6 variable containing the frequency you wish to tune to, then set a RR variable with that vb6 variable. The next portion writes that frequency to a "temporary" fm preset. Then you run a wait exec to insure the file has been created before using it in the last command which simply loads the preset. Let me know if you need me to break it down further but it does work and has worked for me for some time. My skin just has a number pad where the user has the option of dialing a station directly and thats how i handle it.
SETVAR;FREQENTER;" add _root.FREQENTER add "||WRITETOFILE;$RRPATH$DTUNE.fm;=$FREQENTER$||WAITEXEC|FMPRESET;DTUNE