I've been experiencing this since RC2. Now I'm on the retail version of Home Premium I have exactly the same problem.
Every reboot causes loss of Internet and many drop-outs (as described by you) during Internet usage.
I know it's not my ISP or Box, it seems to be related to Windows 7 and Nvidia Nforce.
I've tried all the different Nvidia Nforce drivers
and still have this extremely frustrating problem.
To date, it is my one and only 'f**k Windows 7' problem!