ConCat

ConCat/Split is a Windows Explorer context menu extension that provides two complementary facilities:
A split facility that lets you easily convert a single large file into several smaller ones.

You can copy these smaller files onto removable media such as a memory card, floppy disks, or CDs, or send them through email systems that will not allow large attachments.
A file concatenation facility that performs the same operation as the command line "copy /b SrcFile1+SrcFile2 [+SrcFileN] DestnFile" operation. With ConCat, you can append any number of files and store the result as a new file, or overwrite one of the original files.