An md5 sum file does not go into the iso. It is used for verifying that the volume digest (in this case the iso) has not been modified.
Here you go, in plain english:
1. download Iso.
2. download md5 checksum file.
3. md5 iso and make sure the iso you downloaded matches the md5sum in the md5 file.
if the checksum doesn't match, re download from a reputable source (repeat steps 1 -2 again ), until you find an iso that matches it's md5 sum
4. open iso with winiso to ensure it is indeed bootable. If it isn't find an iso that is bootable and repeat steps (1-3)
5. burn iso to cdr media
6. install
Note: Some Cd's that are indeed bootable will not boot in some Cd-rom drives. I have run into this issue once in my life.
Try booting to the CD from another computer to ensure that the image works period.
If this is the case, upgrade your cdrom, or swap your cdrom with a cdrom that works (which requires familiarity with ide buses, and some moderate pc repair skills).
If all else fails head over to
http://www.freebsd.org, and download a real operating system, lol
