Internet Explorer 7 has many new security-related features on Windows Vista and Windows XP, but the most important work only on XP. IE runs, by default, in a crippled mode called Protected Mode. Doing bold and possibly dangerous things will require special permission. It's a special type of User Account Protection for the browser.
And as with User Account Protection, it has the potential to trip on the outstretched leg of social engineering. Even if it works perfectly, all you need to do is convince users that they really do want to do the things that Windows is warning them could be dangerous. IE7 has plenty of other cool and useful security features, but they also all happen in Windows XP.
A good example of a feature that has been around for a while is NAP (Network Access Protection), which came out, I believe, for Windows Server 2003. It is a set of programs and policies, similar to Cisco's Network Access Control Program and the Zone Labs Integrity product line, that defines security and other requirements for a client before it attaches to a network. The requirements can be that Windows be up to date with specific patches, that anti-virus software be running and up to date, that other programs be installedjust about anything.
The advance in Vista may be as simple as bundling the client components of NAP, but it would be good if this encourages use of it. I have a dream that one day a system like this will be simple enough for ISPs to use and thereby keep dirty clients off of their networks, but we're nowhere near there yet.
There's a lot more, of course: The Windows Firewall will finally filter outbound traffic. EFS disk encryption will improve. Windows programs can be profiled so that the system will know what resources (such as TCP ports) they use, and anything else will raise a red flag. Microsoft's malware removal tool, which runs during updates, will be included. Many of these are important, and I'm sure I'll be looking at them in greater depth in the coming months.
This isn't the first time Microsoft has gotten serious about security, so it would be premature to declare victory against security threats, and Microsoft is plenty circumspect about the future of such things. There is some clever stuff here though, along with a continuation of a several-year trend of locking things down after an orgy of opening insecure services in the late 1990s. If all Windows users were running Vista, the Internet would be a much safer place.