Go to market download RyanZA's OCLF. Also download Quick Boot, by Sirius Applications Ltd. Run RyanZA's app and select root 2.1 which will show up as a green selection. It will ask, or force a reboot. Since it sounds like you have one of the Captivates that the button commands do not work just let it reboot. Once you have rebooted. Open up the Quick Boot app and select Recovery from the menu. It will now reboot again and this time bring up the recovery console. Use the volume buttons to scroll down and select install packages.
If this doesn't work, you will need to boot in to recovery by using adb shell. This is a program for windows that you have to run from the command prompt. It is available by downloading the android-sdk-windows.
Open up command prompt, from run button in windows type cmd. This will bring up a command prompt window. Change to the directory where you unzipped the sdk.
For example if you unzipped it on your desktop you would type, cd c:\Documents and Settings\yourusername\Desktop\android-sdk-windows\tools
Once there make sure your phone is plugged in via usb with usb debugging checked.
Now back to the console, type adb and hit enter. This will bring up all the command lines you can use.
In your case type: adb reboot recovery If you get an error, try typing adb start-server then hit enter. Then retype the adb reboot recovery again.
Good luck.