Can someone tell me why my Custom Icons work in Street Pilot but not in Nuvi?

What do you mean by "Messed Up"?

Try sticking with the same icon sizes as MapSource, which says in part in its Help about custom waypoint symbols: "These symbols must be in .bmp format... Custom waypoint symbols can be 16 x 16 pixels (small) or 24 x 24 pixels (large) and up to 32-bit color." I cannot find how many colors a nuvi screen displays, but 256 color should work for most any Garmin.

Maybe it has something to do with the odd size. Also not sure what you mean by 73.00 resolution, because postscript standard is 72 dpi, but I think that is just a standard printing size thing.

A nuvi will not properly use 32 bit color icons (they may display but there will be no transparency). For a nuvi be sure to save the bmp in 256 color (aka Indexed color) mode. The magenta color (r=255 g=0 b=255) appears transparent on the nuvi, allowing for non-rectangular looking icons. Keep the size to 24x24 or under, and make sure that at least one of the dimensions is an even number.

bmps display fine on the nuvi this way, I've made several that work great.

Ok.
What creative program is a good program to make the icon, I use Paint.Net. How would you know what color mode you are in? I tried Efflandt wrote and swithed my DPI from 73.00 to 72.00, but I am not sure how to change the color mode...

Photoshop is great but expensive (I have an old and limited copy that was included with some hardware, but it does the job, couldn't afford a new copy). One graphics tool that I like very much is irfanview from http://www.irfanview.net/. It will reduce a file in larger color space to 256 colors (use image, decrease color depth ...), but isn't a great tool for creating the icons (no easy way that I can find to create the magenta color and rather limited painting tools). One tool that I would expect to work fine and is free is Gimp. I'll have to download and try the current Windows version. The UI is a bit different from the typical windows program, but It's a great graphical editor.

Thanks guys I got it. I went back to Windows Paint and done as said in some replies above. I changes the DPI to 72 and I swithed the color when I save it to 256 mode, and it worked. Oh and I also made wide and height the same. So I am not sure which one made the change but it worked..The other icons that I said were working are still working with no changes. Thanks

72 dpi should not matter, mine are certainly not set to 72 dpi and work fine. Dimensions don't have to match (I have made a 12x24 one that works fine, but I have seen a warning not to make both dimensions an odd number, not sure if odd numbers really causes a problem or not).

You don't have to go to Windows Paint, Paint.net can certainly create them ok, when you save a project as bmp, it will ask you to select how many colors, 8 bits is 256 colors.

I think that an older version of Paint.net used to default to more more colors, so that would explain why it only worked when you went to Windows Paint, maybe you are using an old version of Paint.net, I am using v3.36 and all the icons I create work just right.

Just in case anyone had any doubt, Gimp does indeed create these files just fine. A current windows version is here:
http://gimp-win.sourceforge.net/stable.html

Are you familiar with Paint.net? if so, how do they (Gimp and Paint.net) compare?

See http://www.poi-factory.com/node/11233

Still not sure, particularly after seeing spider write "I have no idea why this is, since not all icons with odd number of pixels come up scrambled.". It certainly could be some other problem that someone came across and interpreted as an odd-number issue. But since I had seen talk of this it seemed better to mention that it might be an issue than to completely ignore it.