If you're trying to manage the other machine using the basic management tools, you can just right click your 'my computer' and select 'manage'. Then when that opens, right click the top node "Computer management (local)" and select "Connect to another computer".
If you want to use vanilla MMC and add your own snapins, you would run MMC, File->Add/Remove Snapin, Add button, then select what snapins you want (bearing in mind that some of them can't be used remotely, like Defragmenter). For example, select Event Viewer and click the Add button. Another window pops open, and asks you which computer you want to manage. Click "Another computer" and then type in the computer name or IP, then hit 'Finish'. You can then add more snapins as you choose, or close the Add window and use the snapins you selected.
If a snapin does not pop up the "Which computer do you want to manage" window when you select it, then it most likely can't be used remotely.
Likewise, if you want to edit the registry on the other computer, open up regedit, go to File->Connect network registry.
This will only work if the Remote Registry service is running on the other machine.
Btw, something I find VERY handy for remote management, is the PS tools from SysInternals:
http://www.sysinternals.com/Utilities/PsTools.html
Mainly for PSExec which allows executing programs on remote machines. If you want to see remote machines task lists and even kill tasks (including tasks that you can't normally shut down), use the built-in windows command "tasklist" and "taskkill" - by default they operate locally, but with a few command line switches they will work on remote machines (Use /? for syntax).
