HTC S620 used as a modem - unsuccessfully.

Question

The instruction book says I can use the phone as a modem, to give internet access to the asociated PC (a Toshiba Tablet running XP Pro to SP3, in my case).
The book says the phone to PC link can be either Bluetooth or USB cable.
For the Bluetooth, I've paired the phone to the PC, then invoked Internet Sharing on the phone. At this point the phone tells me to set the PC to the Bluetooth PAN. I do that, and both the PC and phone give their status as 'connected'.
However, the PC browser cannot connect to the Internet (AKA get any response from Forums or standard company sites like the BBC). While both pieces are in this connected status I can open up the Browser on the phone and connect to the Internet.
Connecting the phone and PC together via a USB cord, and invoking Internet Sharing, is simpler, apparently successful, but also ineffective as far as accessing the internet from the PC.
I'm wondering if I'm missing some vital step in setting up Internet Sharing.
Has anyone else ever managed to use the HTC S620 as a modem?
I have tried the BT Helpdesk, who suggested the problem was with the phone (reflecting my opinion).
I've asked HTC (0845 890 0079) and they have gone away to investigate, returning after a couple of prompts to suggest I do a cold reset on the phone. This smacks of desperation, with no guarantee of success, and I'm not sure what additional workload this will give me in terms of rebuilding it back to it's current state, applications installed, etc.
I've looked if I can upgrade or update the Windows Mobile 6 operating system.
I see the current is 6.5, but I need to install 6.1 first. After failing to install 6.1 from Microsoft US (with an error message saying invalid lanuage setting) I enquired of HTC, who tell me the S620 phone will not support 6.1.
Cynically, I'm not sure whether to believe them, although it wouldn't be the first time I've met an error message that was inaccurate.
Does anyone else care to comment about running 6.1 or 6.5 on the HTC S620?
As you can see, I've given the problem some attention before asking for help, but that's what I'm asking for now :-)
Thanks.

Answer 1

Thankyou both.
I wanted to use the phone as a modem 2 or 3 times a month, and while the facility is 'nice to have' I'm not sure about investing in a newer smartphone.
I think I'd rather spend money on a pure Internet access dongle for the PC, either a plug-in or more likely one that sets up a small WiFi network, like those availble from the Three network.
I just have a suspicion that a dedicated device will give better service. I'll accept poor service if it's free (built into a device I already have) but if I'm going to have to pay then I'd rather get the best (most suitable / cost effective) device I can.
I do have the 10MB per month allowance, most of which is wasted each month, so I do have some headroom for experimenting with the phone. Currently my mobile bill is 00.00 per month as I never go over the limit of the speech or data allowances.
Of course, if I bought such a dongle I'd also be buying another data allowance, so the 10MB / month on the phone would still be wasted.
After making my original post I found a forum that seemed to have lots of posts, over a considerable time, relating to upgrading the S620 to 6.1 or 6.5. Some of them seemed to claim speed benefits through better design (compared to v6.0).
http://forum.xda-developers.com/search.php?searchi​d=45063678
At this point it helps to understand that the S620 is also called the Excalibur.
As MarkV mentioned, I did wonder what I was going to lose by crossing to the wrong side of the tracks. I don't use BT Talk at all, in fact BT have withdrawn the service from me. At least, that's my understanding. It's no loss at all, to me, so I'm not bothered. I'm not really sure what else I'd loose. Probably all those applications shown as BT something, which I've never used anyway!!
I've almost convinced myself to experiment :-)
Thanks again.