Ok, you're either going to hate that I'm pointing this out or you're still going to be confused.
RAR is a file compression format like ZIP (or StuffIt SIT files if you're a Mac user). You need a utility such a WinRAR to uncompress the files archived within. If you downloaded the X2CL 5035 RAR file there will be 4 files inside I think. 2 .BIN BIOS files, one which is for 1.0-1.5 Xboxes and one that is for 1.6+ Xboxes. The other two files are the readme/changelog and and LBA48 information file. There may be more, but the important ones are the .BIN files. You want to select the right one for your version of Xbox and then flash the BIOS with that file. You'll see that these two BIN files are both 512KB and properly sized for flashing.
After you flash be sure you select bank 1 on your switches. FlashBIOS always starts writing on bank 1, so if you have bank 2 selected and leave it selected you will still see FlashBIOS loading.
BTW, I would recommend only getting files from Xbins. Files picked up via P2P sharing cannot always be trusted.
-Whoopin'