Windows 7 uses a delayed process to start some of it's drivers where Windows XP did not. In Windows XP everything was already loaded before the desktop was displayed but in W7 Microsoft tries to make it appear like you are up and running before all the drivers have loaded. This was done primarily because people complained XP took to long to boot.
Is this what you are referring to? The 30 seconds or so after the W7 desktop is displayed on boot-up before the LAN drivers all get loaded into place? If you are using a wireless connection then this is even more noticable because it takes some time to establish the connection and it all happens after you see your W7 desktop.
If that is what you mean then it is perfectly normal, just a change to the way drivers load between XP & W7. Please mark this solved if that answers your question or give more details if it does not.