i accidentally changed the network setting from a domain to a
workgroup in windows xp professional. now when i rebooted the computer
and put in my username and password, its says something along the
lines of windows cannot verify the login username and/or password with
the workgroup or domain...

that was the only change i made going from domain xxx.xxx.xxx.xxx to
workgroup, none of the domain and wins ips were changed. how do i
revert back to the domain? i also tried to boot up in safe mode but
when i pressed the f8 key, the only option was the standard boot up

On the login screen, there should be a button you can click, I think
it's labeled "Options" that will display what domain/workgroup you are
logging in to.  It will let you change that to your local machine
login.  Login as administrator to your local machine, right click on
my computer and hit properties.  The option will be under there.

If you don't know the local admin password, you will need to reset it.
 You can do this using the following boot disk:
http://home.eunet.no/~pnordahl/ntpasswd/

i know what you are referring to but the options button only seems to
allow me to shutdown or restart. no addition fields show up.

You disjoined from the domain. You can't rejoin unless you're
connected to the domain. To get back on do the following:

Make sure you're connected to the domain, either with a cable connection 
or wireless (cable is better). 
- Log onto your computer with a local administrator account. You created the
password when you set up the machine. That will allow you to log onto the 
computer locally.
- When you're logged on, right-click on Computer, selected Properties, 
choose Computer Name, and click on the Change button. You need to enter 
the domain name (shouldn't have to enter the full name, just the first 
part before the first period).
- Click on OK, and you'll have to have an domain admin account login name 
with the password. Enter those and click on OK. 
- Give it a few seconds (maybe longer), and you'll be back on the domain.

Now you should see the domain name listed when you are at the login page 
and click on Options.

Everyone has posted good comments on this one, but there are some
things that have yet been mentioned.

First thing you MUST do is log into the computer as a local machine
administrator.  You will find when working in domains, you can add
Domain Accounts as administrators on the machine, but you also have a
machine account as a local administrator as well.  For example the
Administrator account is one of them.  If you are unsure if the
account your are utilizing is a local machine administrator, right
click My Computer, go to Manage, In the Management Console, click the
Plus sign beside Local Users and Groups, Click Groups, then
double-click Administrators on the right.

This will show you the local machine accounts you can utilize to have
the access needed to switch back to the domain.  If you cannot log in
as one of these accounts, google a windows xp password cracking app. 
They typically make a boot disk and you can change the password after
booting with the floppy they make, the guy mentioned this in another
post.

Anyways, connect your machine to the network where the domain
controller resides.  If you are a system administrator, it would
probably be best to remove the comptuer from the domain in "Server
Manager" if NT Domain, or in "Users and Computers" if an Active
Directory Domain; if you are not a domain administrator, then have
your admin try that.  If in Active Directory, add the computer with
the name of your choice to the domain, and change the name of your
computer to match by right clicking my computer, properties, and
clicking computer name tab.

Here you can change your computer name and domain membership; click
the change button.