Looks like version 1.1 of the .NET Framework fixes the problem with the error "invalid index..." when using the ASP session object within ASP.NET. This is probably the best way to save state when using ASP or ASP.NET with .VFP. unless you're scaling the app across multiple web servers(in which case sessiontable is the way to go). You might want to change your code from SessionTable to just plain Session. For example:
Change -

lnCount=NVL(oSessionTable.VALUE("count"),0)
lnCount=lnCount+1
lcHTMLout = STR(lnCount)
oSessionTable.VALUE("count",lnCount)

TO

lnCount=NVL(oSession.VALUE("count"),0)
lnCount=lnCount+1
lcHTMLout = STR(lnCount)
oSession.VALUE("count",lnCount)

The only small problem with sessiontable is the fact that it uses a Memo field which can get pretty big and might have to be maintained on a busy site.