i dont have a monitor keyboard for my desk top computer. can i open it with my laptop? if so how?

No, not directly like a monitor unless you have a video input device for your laptop.

If you have the Pro version of XP/Vista/7 then you can enable remote desktop and then log into it that way.

If you have the home version you can install VNC or similar to share your screen over the network.

Hook the systems together via a router and a couple of ethernet cables. I would use a program like Dameware Mini Remote Control to visualize the desktop as mentioned above. The advantage of Dameware is that you can remote install the software on the target once you get the IP address. You will need to use a user account that has admin on the target system.

This is a bit involved so I have to ask what is the purpose of getting to the desktop? If it is just to copy over files the it would be easier to pull the hard drive from the old system and put it in an external USB enclosure. You can then copy whatever you need.

http://www.dameware.com/

I've used VNC for this purpose before... it works pretty well.

LogMeIn.com is also an option.

Of course you still need a keyboard, mouse, and display to see what you're doing on the host machine to install either of these...