First off, i wanted to say nice site. I've found it useful for alot of my problems. I've recently contacted Fyodor, and another nmap user about this issue. Of course, Fyodor is too busy to answer, and the other user hasnt been able to help with my situation. Here's the problem:
Current OS: BackTrack 2 (Figured You'd Need This Info)
Nmap Version: (Tried 4.20 Standard With BackTrack, Now Installed 4.22)
I'm running scans on 50 hosts at a time, scanning the 4th Octet of the ip address. The Command I'm using is provided below:
nmap -p 21,42,445,1433,1434,3389,5900 -P0 -T Insane xxx.xxx.xxx.1-50
My issue is nmap is returning invalid results, its telling me all of the ports are open on each individual machine. Why is this? All help/suggestions are appreciated. Thank you in advanced.

Chris Gates, I'm a fan. Contacted you through e-mail earlier today about msf 3.1, disregaurd that e-mail. I'm on a laptop. Linksys Router, I am scanning outside of the subnet.

Well the basics of what i'm doing is scanning a range of hosts for vulnerability. If i scan single hosts at a time of course it will be slower. Thanks for your reply jimbob, i'll attempt the -T4.