(I just posted this on another thread - sorry to be redundant. I just want to make sure everyone gives it some thought.)
I would love to have a slice tool, too, and here's why.
If you check out my website at http://www.nathanlongmusic.com, you will see that there is an image with a little mp3 player embedded.
The way I made that page was:
1) I designed it visually in Adobe Illustrator
2) I exported the whole thing as one image
3) I sliced it up in Photoshop (which I had access to then but don't anymore).
(The "slicing" part means that I drew boxes around each menu item and other chunks of the image, and around a little blank area at the bottom where I wanted to put the mp3 player. Each slice was given a number by Photoshop. When I exported, it created a little subdirectory which contained each slice as an image (1.jpg, 2.jpg, etc) and an html file that displayed them all in a table so that they fit together seamlessly.)
Then...
4) I found the slice of blank space that I wanted to replace with an mp3 player and figured out its dimensions
5) I created a skin for the player with those dimensions
6) I edited the HTML table to replace that little image with my player of the same size, and to make the menu items into links to other parts of the site
Even if you're not creating a custom skin, I have found that designing a menu as one image, then slicing it up and making links out of the pieces, is a way that lets me get a page that looks just like I want it. I can separate the "how do I want this to look" part of web design from the "how do I want this to work" part, which is mostly coding.
So: I would REALLY like to have a slicing tool in Paint.net. Other than that, I love the program.