Hi Matt,
I think the most likely problem with your bmp files is being of the wrong internal format (i.e. bit depth etc). The map component seems quite fussy about what it will import. Anyway, here is a description of how I got some success with the Miniscale data.
1) Download the OS Miniscale data - you  will find the link on this page: http://data.gov.uk/dataset/os-miniscale.
2) The file you have downloaded is a TIFF-LZW, meaning that it contains LZW compression. Our map control only supports uncompressed TIFF, so we need to convert it. I used the GIMP image editor (http://www.gimp.org/windows/) but it should be possible to do this in most image editors. I simply unzipped the download and browsed to the Miniscale\Data folder. There are 4 tif files provided, with or without grids and relief. Pick one, open it in your image editor, then select Save As and choose the TIF format, with the uncompressed sub-option and save the file in a temp folder. It will create a pretty large file of about 260MB.
3) Now in Recorder, open the Map Window. Right click in the Map Layers list and select Add Background Layer. Then, specify the following:
Name: MiniScale
File Name: pick the uncompressed TIF file you created. When you do this, in the File Open dialog you do need to select tif in the Files of Type drop down selector, because for some reason tif is not included in the All Files filter (!).
South-West: SV00
North-East: JM9999999999
Cut-in: 1:100,000,000
Cut-out: 1:25,000

Then save the layer. You can of course tweak these settings depending on your requirements, other layers etc but it should give you a reasonable starting point.

Unfortunately this will slow down initial loading of the map a bit, though I have found that once loaded it runs fine. Of course this may well be dependent on the amount of memory on your machine. If performance is a problem, you could try creating a crop of the image for just your region and using that instead.

Cheers