If this is a roaming profile in a domain setting you can only copy a Domain profile if you are a member of Domain Administrators.
This is a security issue in that the roaming profile is tied to the SID, and duplicating SIDs is a security issue.
The standard fashion of doing the copy would be to create the new user profile, and then:
Log on as a user other than the user whose profile you are copying files to or from.
Locate the C:\Documents and Settings\Old_Username folder, where C is the drive on which Windows XP is installed, and Old_Username is the name of the profile you want to copy user data from.
Press and hold down the CTRL key while you click each file and subfolder in this folder, except the following files:
Ntuser.dat
Ntuser.dat.log
Ntuser.ini
On the Edit menu, click Copy.
Locate the C:\Documents and Settings\New_Username folder, where C is the drive on which Windows XP is installed, and New_Username is the name of the user profile that you created in the "Create a New User Profile" section.
On the Edit menu, click Paste.
Log off the computer, and then log on as the new user.