I'm not 100% sure if this should go here or the main Stack Overflow, but I decided to go with this area in hope I might catch someone with more specific experience with a similar problem.
I have a Samsung Captivate (love it minus it's crappy GPS). I do development for it from 2 different computers, one at home, one at work. The machines are both Windows XP, Service Pack 3, 32 bit. I have the same Samsung drivers installed, same versions of Eclipse, etc. The phone is currently rooted running the Serendipity mod, though this issue was exactly the same on the stock firmware.
My home machine (the problem one) is an Athlon 64 2.2 Ghz. My work machine is a Core 2 Duo, don't recall the model.
At work, I can do anything, mount the sdcard on the phone and copy easily, use adb to push, pull, uninstall, install. I can debug in ddms, install through Eclipse, etc, etc...
At home, if I reboot both the computer and phone and pull up a command prompt without having Eclipse open, I MIGHT be able to see the device by typing adb devices. Usually then, I can clear the logcat or run the logcat fairly stable. If I open Eclispe (my development IDE) and try to run a new build of an app, I'll generally lose the connection. The same thing happens if I try to copy files either via mounting or using pull with adb. Some files will copy, and suddenly the connection will be gone and the device will show offline to adb, or not in the list at all, or listed offline twice. Rebooting the phone sometimes helps, but not always. There are times I close Eclipse and every other app, reboot my phone and still end up having adb completely unable to detect the device. I'll use adb kill-server and adb start-server but this generally doesn't help. I use Avast for my anti-virus at home, but have tried without any anti-virus installed at all and it's the same. I've recently reinstalled Windows due to a hard drive crash and it was the exact same. I've tried every different USB port on my tower.
I hope VERY much someone can tell me what's wrong as I've been dealing with this for a year and a half now and it's about to make me lose my mind.