I had/have the same problem with BO-1. Just bought BO-2 today

and it seems to load up good. Maybe 15-20 seconds from the time the map name shows up. I just defraged before i installed it tho. Check out some programs like:
1: Puran Defrag. <--- Quicker than windows defrag.
2: Memory Cleaner. <-- Set it to clean RAM every 5 minutes works good.
3: RAMMap. <-- awesome!
4: CCleaner. Meh.
--
Reinstall DirectX from BO-2 disk if you have it.
Close ALL unused programs running in the background -- Windows Update slows me down a lot!
Definietly make sure "Tablet PC Input Service" is closed! You dont need it.
Assumming you have Win 7... Google something like "Windows 7 background services that aren't needed" or something like that. You'll probably find that
, on a fresh reboot, you're running about 45-50+ services when windows starts. You should only need maybe about 30 of them. anyways... Thats what i did and cleared up a bunch of MUCH NEEDED RAM. I only have 3gb to start with! Hope some of ^that helps cause i know i was pissed with all the waiting 'n waiting...