One of the improvements that Microsoft is touting for Vista is a new TCP/IP stack that natively integrates wireless networking. The last time Microsoft reworked the TCP/IP stack for the OS was in Windows 2000. At the time, I noticed some definite improvements in performance over the TCP/IP stack from Windows NT 4.0. Naturally, I expected the same kind of improvement with the new TCP/IP stack.
Overall, I hadn't noticed much of a difference in the networking stack while working with the early builds of Windows Vista -- although I admittedly haven't done much that requires a large amount of data throughput. However, after installing Vista Beta 2 on a Dell Latitude X1 laptop, I quickly discovered a drawback of the new Vista networking stack. When I booted Vista Beta 2, the X1's integrated Intel PRO 2200BG wireless card suddenly did not have as good a range as it did under Windows XP (using the native Windows drivers from Microsoft in both cases).
In a spot about 30 feet away from the access point (with multiple walls in between), where the laptop had previously received a good to excellent signal under Windows XP, it could no longer pick up a strong enough signal to connect to the access point under Windows Vista. Strangely enough, under XP the laptop could only pick up one or two other unknown access points within range. Under Vista, it could now detect up to four other unknown access points within range.
It could be that Vista's networking stack is more connection-sensitive and does not like to connect to mediocre signals, but it can pick up and identify faint signals more easily. I'm not sure. I'm working with some folks at Microsoft to try to get to the bottom of this and I'll report back when I know more.