The PIC 18F4550 is a chip very similar to the 18f4520, differing in one important respect: it has a built-in USB transceiver, so you can do USB communication with it. See USB communication with PC or USB Bootloading.
The PIC 18F4553 is different from the 4550 in only one respect: it has a 12-bit analog-digital converter (ADC) as opposed to a mere 10-bit one. Code written for the 4550 will likely run without changes on the 4553, and vice versa.
Programming the 18f4553
If your version of the CCS compiler does not list the 4553 as a supported device, you can just program for the 4550, which is almost exactly the same except that it has only a 10-bit ADC. However you will need to update your ICD firmware so that it recognizes the PIC. Save this file to your "C:\Program Files\PICC" directory: [Image:icd-images-firmware-02-51.fw]. Then plug in your ICD and run "C:\Program Files\PICC\icd.exe". Click "Update Firmware", then select "Other" and browse to the file you save. Then hit "Ok" to update the firmware.
If you're programming for the 18f4550, when you hit Program in CCS you'll need to confirm that it's OK that the code wants a 18f4550 while the detected target is a 18f4553.