Questions Regarding Networking

I've got a few questions regarding networking in general and then some issues that have popped up since upgrading (in place) to Windows 7.

1) Generic question: If I were to install a Wireless N router would the wireless network default to the slowest connection on the network? For example, if I had two N wireless adapters and one B adapter would the entire network run at B speeds? If so, would a dual band router allow me to circumvent the issue?

2) Generic question: Would the same issue as outlined in #1 be a problem in a wired network? Can I mix 10/100 and gigE on the same wired network and achieve gig speeds between gig-enabled devices?

3) Specific: I have an HP dv9500t that I upgraded to Windows 7. HP has not released Windows 7 drivers for this machine but I have been able to work around the few issues that I encountered. However, my wireless connection to my Linksys AP (Wireless-G broadband router WRT54G2 with up-to-date s/w) seems to be dropping and recovering on a regular basis. I have not seen the issue on any other wireless network. If I am downloading a large file (say 1G) the d/l will proceed at full speed for ~45 seconds and then drop to zero for ~45 seconds. I'll usually get the "limited connectivity" alert but then the link will restore itself and begin transferring again.

I've run some of the Linksys diags when it is down and it usually tells me that the default gateway is unavailable and resets my wireless adapter and the whole routine starts again. Quite frustrating. I've worked with Linksys tech support (they claim no known issues with Windows 7) and their supposition is that it is an interference issue and they suggest I change wireless channels.

I've tried 6 different channels and the issue does not change. I have tried upgrading the adapter drivers the the latest available from HP (Vista drivers, not Windows 7) and have also tried drivers from the adapter manufacturer (Intel Wireless WiFi link 4965AGN, Win 7 drivers) but the issue is still there. I have also rest my AP back to factory defaults to no avail. It certainly could be that I have burned through yet another wireless AP but before replacing it I wanted to see if anyone might have suggestions.

4) Since, as far as I know, Homegroup cannot be used unless all of the PCs on the network are Windows 7 I am trying to utilize Workgroup settings to config my network. The problem is that my wirelessly connected laptop does not seem to have access to my wired workgroup unless I set the SSID of the AP to the same name as my workgroup. Is this normal operation or is there a good tutorial around showing me how to set this up?