Add a new user in Windows XP, Vista.

Create separate accounts for each person using a computer. Each user has its own settings, files, wallpaper, Start menu (Start),visual style, etc. If your computer is in a workgroup follow these steps. 

In Windows XP 
1. Start. 
2. Control Panel. 
3. User Accounts. 
4. Create a new account. 
5. Enter your account name. 
6. Next. 
7. Select the desired account type (Administrator or Limited if you want to increase or decrease the user rights). 
8. Create Account. 

In Windows Vista 
1. Start. 
2. Control Panel. 
3. User Accounts. 
4. Manage another account. 
5. Create a new Account. 
6. Enter your account name. 
7. Select the desired account type (Administrator or Standard if you want to increase or decrease the user rights). 
8. Create Account.