XNA doesn't have any direct support for tile maps so you'll have to write an importer or loader for whatever map format you use.

Tile Studio is a freeware program for creating 2D maps with tilesets.  It's not perfect but it does everything you need and the price is right!  ;-)  Another nice thing about it is that you can write your own exporter to save the maps in whatever format you want.  I wrote one to save maps in the format used by XNAResource's Tile Engine Tutorial.  Let me know if you want me to send it to you.  Between Tile Studio and the Tile Engine Tutorial code, you'll have everything you need to create a map and load it into your game.

Tom

Sorry for the delay in getting this to you.  Since it may be of use to others as well, I'm going to go ahead and post it rather than email it.

; --------------------------------------------------------
; Tile Studio Script for XNA Tile Engine Component
; from www.xnaresources.com
; --------------------------------------------------------
#file <ProjectName>.map
#tileset
#map
1\n<MapHeight>\n<MapWidth>\n
#mapdata
<TSBackTile>\n<TSMidTile>\n<TSFrontTile>\n<MapCode>\n
#end mapdata
#end map
#end tileset
#end file

Put that in a file called XNA.tsd in the same directory as the Tile Studio executable.  Once you have created your map in Tile Studio, go to the Code->Code Generation Settings menu item and select XNA.  Then select Code->Generate Code to create the file containing the map.

You can load it into your game using the following code from XNAResources Tile Engine Tutorial:

        void ReadMapFromFile(string sFileName)
        {
            StreamReader srReader;
            srReader = File.OpenText(sFileName);
            int iReadVersion = Convert.ToInt32(srReader.ReadLine());
            iMapHeight = Convert.ToInt32(srReader.ReadLine());
            iMapWidth = Convert.ToInt32(srReader.ReadLine());
            for (int y = 0; y < iMapHeight; y++ )
            {
                for (int x = 0; x < iMapWidth; x++ )
                {
                    iMap[y,x] =  Convert.ToInt32(srReader.ReadLine());
                    iMapTrans[y, x] = Convert.ToInt32(srReader.ReadLine());
                    iMapObjects[y, x] = Convert.ToInt32(srReader.ReadLine());
                    iMapWalkable[y, x] = Convert.ToInt32(srReader.ReadLine());
                }
            }
            srReader.Close();            
        }

BTW, you may also want to check out this thread that has information about other 2D tile map editors.  I used Tile Studio because it was all I could find at the time.  It met my needs but I'm not completely happy with it, so you should check out some of the others too to decide what you like best.

Tom