I have a TP2 now and tether with wmwifirouter. I have never had to do any editing/hacking of the reg or had any of the issues you describe but then I never tried to use ICS alone on TP2. My advice would be to download the free trial and see if that helps.
http://www.wmwifirouter.com/
I used to tether with my SPrint Mogul, first with just ICS in windows but had constant dropped connections. Then tried PDA net and had similar issues. I thought the newest PDAnet version might help so I purchased it but same issues. Still waiting for my refund.
Then I got wmwifirouter for my Mogul and it was like a beautiful dream. It worked 99.5% of the time. The difference in reliability between ICS and wmwifirouter or PDAnet + Activesync vs wifirouter cannot be overstated. Did I mention I really like wmwifirouter?
wmwifirouter doesn't depend on crappy Activesync on the PC side to function which may be part of the difference.
As for PDAnet, I used to save the error messages and email them to the company periodically. Eventually I ran out of hard drive space.
Connecting to your Device...
Connecting to Data Network...
Verifying User Name and Password...
Dialup failed, error=619 (state=8193)!
Connecting to your Device...
Connecting to Data Network...
Verifying User Name and Password...
Dialup failed, error=31 (state=8193)!
Connecting to your Device...
Dialup failed, error=797 (state=0)!
Connecting to your Device...
Connecting to Data Network...
Verifying User Name and Password...
Dialup failed, error=31 (state=8193)!
Connecting to your Device...
Connecting to Data Network...
Verifying User Name and Password...
Dialup failed, error=619 (state=8193)!
Connecting to your Device...
Connecting to Data Network...
Verifying User Name and Password...
Dialup failed, error=619 (state=8193)!
Connecting to your Device...
Connecting to Data Network...
Verifying User Name and Password...
Dialup failed, error=619 (state=8193)!
Connecting to your Device...
Connecting to Data Network...
Verifying User Name and Password...
Dialup failed, error=619 (state=8193)!
Connecting to your Device...
Connecting to Data Network...
Verifying User Name and Password...
Dialup failed, error=619 (state=8193)!
Connecting to your Device...
Connecting to Data Network...
Dialup failed, error=638 (state=2)!
Connecting to your Device...
Connecting to Data Network...
Dialup failed, error=638 (state=2)!
PDAnet connection failure 3039
PDAnet connection failure 3033
"cannot connect with the current connection settings. tap "settings" to change" after having been successfully connected for ~5 min
"cannot connect for an unknown reason" after having been successfully connected for ~5 min.
"make sure PDAnet is running on your phone" (it is)
PDAnet connection failure, error 3064
"network connection lost"
PDAnet connection failure 3033
Connecting to your Device...
Connecting to Data Network...
Verifying User Name and Password...
Dialup failed, error=619 (state=8193)!
PDAnet connection failure, error 3064