I'm planning to back up both my CMR 2005 and TOCA 3 to a disk and a separate HD considering they wont be avalable for redownload in the near future. How do I check the integrity of the files after wards? I dont want to find out in the future that my games are corrupted when I need to use them again.

The GOG installer incorporates a basic integrity check. Additionally, any good disc-burning program includes a data verification step after burning so you know straight away that the files you have burned are byte-exact copies of the local files. To do your own integrity check you can use something like HashTab, which adds a File Hashes tab to the Properties window.
For reference, the checksums for TOCA 3 should be as follows (I don't have CMR so I don't know what its checksums are).
setup_toca_3.exe
CRC32: 7E86E7EF
MD5: 8B6D95AD2DF0EFC19309DC75CD233322
SHA-1: DC38029E24046FC9476A20796ED207A3A887FE2D
setup_toca_3-1.bin
CRC32: 39A0D8C2
MD5: 4187245C9D32A7DDD930F26FC75DC58D
SHA-1: D93256F859B620D50239685555B6D6E1B3A027EB
setup_toca_3-2.bin
CRC32: 63ABC971
MD5: 4B3B4235D439A2409DBB108981ABC147
SHA-1: 711F52BB1E42E9A5033A9C1246F5EDA19904136C
setup_toca_3-3.bin
CRC32: 36751672
MD5: D6A5A69F5F6A5506ADAEA2C80835B183
SHA-1: 6BB3A68A363948DCBF409B82EC1E17E89B97E23F

It's a good idea to check because when I tried to install my game today (I'd downloaded the files back when I'd bought the game-so I was unconcerned about the deadline) it turned out that the installer said the last two were corrupted! So now I'm stuck downloading them again (and hoping these copies are OK).

Man, HashTab is the coolest thing ever!
I ran the hashes for CMR, I'll post them in that forum. Strangely though, I got completely different hashes for my TOCA3, and I *think* it's OK. I'm downloading again just to be sure. I wonder if GOG changed the install files since release?
Update: Hm, the original ones I downloaded and installed didn't have the
"Checking file integrity" step. Sooo, while they're probably OK too, it's maybe not as solid though. That would explain the differing hashes, though. I'm going to back up the newer ones as well, might as well have a spare.

Yeah, GOG's installer format originally didn't include an integrated integrity check, and since then they have updated all installers to include one. The integrated integrity check is nice to have even if only to provide another form of reassurance.