computer has about a 10-15 second delay, after start up, connecting to our network. it's not that big of a deal but there are some batch files in the startup folder that require access to network drives. this means the batch files run before they access to the drives.  

i know we can go and edit the batch files and put an even longer time counter in them, but seeing how it's 1 computer of 600 or so that is doing this...  
1) bios and drivers are up to date.
2) switched out ethernet cable and ports in the switch room.
computer is a new optiplex 790 running W7 64bit

I've looked at this post a few times and wondered because I have the same problem on one machine on my much smaller network. My machines are all 32 bit and recently (Year Ago) restored to factory default. I was tearing my hair out like you.

I blamed the NIC card but a new card made no difference.
I blamed a failing hard drive but overnight tests gave it 100% OK

Rather than restore it again, I cleaned it up. 7000 windows junk files, 364MB Internet junk (forgot to re-set the maximum whoever set it up) about 4000 cookies, error reports, set up logs, boot logs and the rest. Sorry, but I do it manually. Empty the recycle bin and defrag. 2 files unable to defrag. msconfig and disable the junk.

Guess what?
I'm happy with 5 seconds.