Using the left and right mouse buttons together to emulate a middle button is called chording. You mentioned a laptop, so I don't know what kind of pointing device you have. Touchpad? Eraserhead? Trackball? Regular mouse?
Before going through that procedure outlined in the Ubuntu forums, I'd try these one at a time. As root, edit /etc/X11/xorg.conf and find this section:
Before the line that says EndSection, copy these lines and paste them there:
# Emulate3Buttons is an option for 2-button Microsoft mice
# Emulate3Timeout is the timeout in milliseconds (default is 50ms)
Option "Emulate3Timeout" "50"
Save, exit the editor, type
to go back to your user account, and type
to start IceWM. Open a text editor and copy some text by swiping with the left mouse button. Then see if you can paste that text by pressing your left and right buttons at the same time. If so, you're done. If not, log out from IceWM, su to root, and edit /etc/X11/xorg.conf once more.
Delete the lines you added before because they don't work. Copy the following lines and paste them in the same place as the lines that didn't worki:
# ChordMiddle is an option for some 3-button Logitech mice
Save the file, quit the editor, and type
to return to your user account. Type
to start up the GUI. Do the same test of copying by swiping and pasting with the left and right buttons together. If it works, you're all set. If it doesn't, I don't know what to suggest. Let us know if either of these works and if not, we'll see if we can come up with something else.
Start in linux-tui mode if you want to try these experiments. The /etc/X11/xorg.conf file is read whenever X is started, so you don't need to reboot, just exit to a text mode console, do any editing to xorg.conf, then run startx to start up the GUI.
I almost forgot: always back up xorg.conf before you make changes. Then, if your changes prove to be disastrous, you simply delete the xorg.conf file and rename your backup to xorg.conf and you'll be back where you were before you made changes.