Here's an interesting quandary...

Howdy,

I'm a network professional having some issues I can't explain, so I thought maybe a few heads are better than one.

System Specs:
Windows XP Pro SP2
512 MB RAM
744 / 1024 MB Virtual Memory
80 gb HDD (50gb free)
Kaspersky AV 7
On a Domain as Admin
Firewall Disabled (Running an external)
T1 Connection

Symptoms:

Slow, often unresponsive network performance.
Slow, often unresponsive local hdd performance.
Very slow boot

Tests / Fixes so far:

• Kaspersky AV 7 (Nothing found)
• Spybot 1.5 (Nothing found but a couple tracking cookies)
• HijackThis (Looks fine)
• Cleared Swap File
• Pagefile is NOT affected, in fact its pretty low
• Nothing visibly affecting resources, will check with PE Explorer
• Mem test from command prompt (Normal)
• Drivers for Ethernet up to date
• Ethernet is onboard so seating not an issue (unless it's a bad connection which I haven't checked)
• Booted with PEBuilder to run Spybot S&D (Couldn't download additional installation files because of network not responding)
• Up in the air whether to just wipe and RF or try reinstalling SP2 at a snail's pace
• Hardware all appears to be in good working condition.

Essentially, I've done mostly everything I could think of before asking for another opinion. This one has just plain got me stumped.

Ethernet is onboard so seating not an issue (unless it's a bad connection which I haven't checked)

You should. More often than I would care to admit I have been frustrated at mysterious network issues only to discover out of desperation that swapping out a $2 flaky Ethernet cable fixed it. They can only be yanked and tripped over so many times.

Slow, often unresponsive local hdd performance.
Very slow boot

Well, these would not be network issues so it would appear you have more than one issue here. Still, I would make sure you have no networked drives mapped, all external devices (USB and Firewire) are disconnected, and that there are no errors showing up in device manager.

Cleared Swap File
Pagefile is NOT affected, in fact its pretty low

Not sure what you mean here - the swap file IS the page file. Nevertheless, with only 512Mb of RAM, it is likely your page file is getting hit - but, unless you've made recent changes (new hardware or software) this problem would have been going on all along.

Even though you've run a memory test, I would swap out the ram just to be sure. It's one common point that networking and hard drive performance have in common. Do you see the same degradation if you boot to Safe Mode with Networking?