Ok so, this is basically what I did (and you can hear what I was able to accomplish doing this here
http://rapidshare.com/files/372135664/voicechange.mp3)
I started much the same as you, just experimenting for a couple minutes very infrequently (though I was like once every month or so because I hated how I sounded).
I never worried too much about the pitch values though. Pitch is only a pretty small part of sounding female, it's far more to do with modulation/resonance of the sound of your voice than the actual pitch. You can use audacity (same program I used) to make the pitch of your voice sound higher, but you still won't sound female, nor would a female sound male in doing the reverse, because there's much more too it than that.
Now, this is just what I did to change my voice as it sounds in the link above. I don't really know if I sound good or not (people say I do but I can't help but feel like they're telling me what I want to hear) and what I did may for all I know not work for you.
I never did much of any "practicing" or "training" or anything on my voice, by the time it sounded almost the same as it does above there, I hadn't even realized. My mother didn't even realize my voice had changed at all until I showed her the comparison, leaving her utterly shocked, because it had happened so gradually over about a couple month timeframe she hadn't noticed any point where it suddenly changed.
What I did, was I simply tried to sound female. Any time I was where nobody could hear me, I would verbalize whatever I was thinking while trying, not very hard but very subtly, to make it sound somewhat feminine to me. If you do that long enough I think the voice muscles just change on their own. Now it's at a point where I can't actually sound like I used too any more even if I try too. I can sound reasonably male if I try too, but not for long periods of time before it slips back, and not in the same way as I used too. I suspect I'd probably have to do exactly what I did to sound female only to sound male in order to get it back again (not that I ever intend to do that

).
So anyway, eventually after doing that for a little while, it started to sound at least androgynous when I wasn't even trying, and androgynous leaning female when I was. It was around that point that I started trying to sound that way not only to myself but also too select people I met around me.
A little while after that it changed more onto the female side of things (i hope, lol, I refuse to say I sound female for risk of tempting god) and it was at that point I became confident enough that it had changed to show my mother audio clips of me before and after, and she was utterly blown away.
My advise would be to forget about pitch, and just try to sound what you think is the most female way you can speak for prolonged periods of time, and just start using it. If not around other people, then just to yourself. Use a recorder if you like to see how you sound.
Another tip I would give, there are some great things on youtube to help you, specifically the advice to go as high pitch as you can do comfortably, and sit there.
But don't worry too much about pitch range. There are TONS of girls with low pitch voices and tons of girls with high pitch voices. Now yes, pitch is a factor, it's not unimportant, and a pitch way outside the norm for your presenting gender will draw attention, although likely not attention that would out you, just attention generally. But what will absolutely make 90% of the difference is resonance, which is the actual sound of your voice, the same sort of thing that differentiates the way you personally sound, as opposed to any body else, also determines the way your gender is read. Far more so than pitch.
In my opinion (and that's all it is, it may very well be a bit dependent on your preexisting vocal characteristics... your mileage may vary), voice training courses are a complete waste of money. I've never taken one, the instructions I used to get started were a couple youtube videos.
This one is the one I usually link people too.