When you need to convert between object file formats, download one of P&E's free, C language development kits.  These kits include a full GNU compiler toolchain, including Binutils OBJCOPY.

Download PKGPPCNEXUS Starter Edition
http://www.pemicro.com/downloads/download_file.cfm?download_id=194

Download PKGCFZ_PRO Starter Edition
http://www.pemicro.com/downloads/download_file.cfm?download_id=180

P&E's ICD In-circuit Debugger and PROG Flash Programmer software, included with the Starter Editions, natively supports several object file formats, including s-record and ELF.  Soon, P&E software will natively support Intel Hexadecimal files.

After installing one of the Starter Editions, run OBJCOPY from the Windows command-line.  The program is located in the gnuin subdirectory within the installation directory.  View the help screen for OBJCOPY from the command-line by typing  "powerpc-eabispe-objcopy" or "m68k-elf-objcopy".  You will see a list of all program options.  To determine which formats are available with OBJCOPY, take note of the final lines of the help screen.  You will use these format names, BFD names, when running OBJCOPY.

To convert a file, use the  "-O" option followed by the name of the desired output format.  The input format may be specified with the "-I" option, though this is often unnecessary.   For example, to convert the object data in a COFF file "file1.coff" to an s-record file "file1.srec":

m68k-elf-objcopy -I coff-m68k -O srec file1.coff file1.srec

or

powerpc-eabispe-objcopy -I aixcoff-rs6000 -O srec file1.coff file1.srec

If you are looking for greater control of file conversion, look at the options on the OBJCOPY help screen.  For example, with powerpc-eabispe-objcopy you may specify s-record length, force S3 records, and manipulate the linker sections in object files.