(elaborating on Bjarney's message)
Software Applications for Image editing will do this .BMP to .JPG type of conversion. The conversion is done when the active (open) image file is being saved. The typical "Save As" Dialog Box in Windows Apps', will have a drop-down box on the lower portion of the "Save As" Window. Drop it down to select a new file format type.
Seems to me also that MS Photo Editor - part of the MS Office 97 (& up) Professional version - can save a .BMP to either .JPG, .GIF, or .TIF.
Applications such as Adobe Photoshop ($$$$mucho bucks!$$$$) and Paint Shop Pro ($$less bucks!$$) are able to save images in many different formats - including metafile types (.WMF).
Used Photoshop a lot for image edits, and liked the results. Lost the Application from a H.D.D. failure, and the CD-ROM original "Ran Away" from home
Currently using Paint Shop Pro, ver. 7. Great results and many capabilities on this Application.
Other Apps' which may perform .BMP to .JPG saves would be ones which come with Scanners (Scanning Packages) and Digital Camera imagery.
Seems like Netscape Composer had these functions too...???