Four minutes start-up is outrageous. I'd check for spyware/trojans, thoroughly clean all junk files, clear all junk entries in your registry and I'd also check your drive for weak sectors.
Regarding anti-spyware, I'd suggest Microsoft Anti-Spyware is better than most packages - and it's free. I got rid of AdAware and Spybot a long time ago. MSAS has an excellent real-time scanner, including monitoring changes in start-up programs. Even if you don't run MSAS resident as a real-time scanner, it will still report any changes in start-up apps since the last you ran it as a manual AS scanner.
As a free system-cleanup utility, CCLeaner is excellent.
The best system cleaner - including excellent control of start-up apps and excellent safety - is the Ace Utilities package. 30-day trial is fully-functional, and price is about $25. It will SAFELY clean your registry, clean junk files, clear your history and provide excellent control of start-up apps. The Ace Wizard will do it all in one pass - SAFELY.
Download drive-test utilities (SeaTools for Seagate Drive and Data Lifeguard Diagnostics for Western Digital drive). Weak read/write blocks can slow drive performance, since multiple passes may be required to read data from weak blocks.
I don't know what you do for Firewall and AV, but there are excellent onl-line virus scanners (Trend Micro, Panda, etc.).
I would do all of the above before considering replacing/upgrading your HD.
Hope this helps!