Here's how to run Duke 3D in DosBox instead of eDuke and still not have lag, for you purists out there:
Go to your Duke 3D folder (usually C:\Program Files\GOG.com\Duke Nukem 3D\ ) and find the file titled dosboxDuke32.conf
Open this file up in notepad, and find
memsize=16
and replace it with
memsize=64
This changes the amount of RAM DosBox allocates. DosBox will read up to 63 Megs of memory total.
This fix is actually pretty universal in most laggy DosBox games, for example, you don't stand a snowballs chance in hell playing any of the free Elder Scrolls games with only 16 megs of RAM.

Nice tip dude! Thanks..

How do I change the memsize? it does not seem to do anything!

it doesn't seem to appear in front of me, are you sure you weren't talking about a file called ''dosboxDuke3D.conf'' ?
i guess i am wrongit denied to mei did it!-------------
\it still lag and are apparent, so, what is eduke anyway?

I can get into the file and change the memsize but when i try to save it it says

"Cannot create the C:\Program Files\GOG.com\Duke Nukem 3D\dosboxDuke3D_setup.conf file.

Make sure that the path and file name are correct."

I have a vista just to let you know.

This is the problem of using the Program Files folder in Vista. Program Files is a protected folder in Vista (and Win7), so it protects the installed files from being changed. In order for it to allow changes you have to run as administrator - it is not enough to just be an administrator user, it has to be the true administrator account which is hidden by default, or you have to run it as administrator. You can also try turning off all UAC but I don't recommend doing this.

The best solution, however, is to never install games into Program Files. Just install to C:\Games or something.

+1, never ever install a GOG into your Program Files folder, GOG installers themselves should better default to a different folder, like "C:\Games" or "C:\GOG" and explain the issue on the installer screen.