Mike,
My ICD2 is the round one - revision 3. I just looked inside and it does have the 4550 in it. I bought it a few years ago but didn't use it as it was painfully slow. When I attached my Unicorn to my Inchworm+ I was pleasantly surprised at how fast it was.
Nye,
The Inchworm is an ICD2 clone. ICD = in circuit debugger. The ICD2 and clones work directly with MPLAB and so no additional software is required. The UBW, or rather the Sparkfun version, has a USB bootloader preprogrammed. Have a read of the site for more info.
Mike.