Create a new user account for yourself:

http://support.microsoft.com/default.aspx?kbid=811151

Create a New User Profile in Windows XP Professional

  1. Log on as the Administrator or as a user with administrator
credentials.
  2. Click Start, and then click Control Panel.
  3. Click User Accounts.
  4. Click the Advanced tab, and then click Advanced.
  5. In the left pane, click the Users folder.
  6. On the Action menu, click New User.
  7. Enter the appropriate user information, and then click Create.

Create a New User Profile in Windows XP Home Edition

  1. Log on as the Administrator or as a user with administrator
credentials.
  2. Click Start, and then click Control Panel.
  3. Click User Accounts.
  4. Under Pick a task, click Create a new account.
  5. Type a name for the user information, and then click Next.
  6. Click an account type, and then click Create Account.

Copy Files to the New User Profile

  1. Log on as a user other than the user whose profile you are copying
files to or from.
  2. In Windows Explorer, click Tools, click Folder Options, click the
View tab, click Show hidden files and folders, click to clear the Hide
protected operating system files check box, and then click OK.
  3. 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.
  4. 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
  5. On the Edit menu, click Copy.
  6. 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.
  7. On the Edit menu, click Paste.
  8. Log off the computer, and then log on as the new user.

Note: You must import your e-mail messages and addresses to the new user
profile before you delete the old profile. For additional information
see 313055 OLEXP: Mail Folders, Address Book, and E-mail Messages Are
Missing After You Upgrade to Microsoft Windows XP

Then you can delete the incorrect user accounts. It sounds like you
inadvertently made your computer a member of a domain. Check in the
System applet under Computer Name. Is your computer still correctly a
member of a Workgroup?

Malke