My problem is with my laptops 'inner clock.' The clock on my taskbar is accurate. I have checked the "date and time properties" and it is set properly. Yet when I receive mail on my gmail account or Yahoo... it is showing time that is 3 hours later. How can I correct this?

If the task bar clock is correct then there isn't a time issue.
This maybe related to time zones though.
Have you set your clock to check internet time to ensure that it is truly accurate and while you're at it make sure you have set the correct time zone.
If everything is right then we need some further information.
You say receiving mail in gmail and Yahoo, but fail to metion if/what e-mail client you are using or if it's web mail access.

My Yahoo email shows PST, two hours different from where I am. To my knowledge, it can't be changed.

Just checked Yahoo and you can change the time zone.
Log in to your webmail > options > account information > the EDIT member information.

I checked my "Account Information" and it has me listed correctly as being in the US Eastern time zone... yet when I look at my Yahoo news it shows the time as 3 hours later :mad:
And I find this problem exists with Gmail and Hotmail. :(

So this is related to the stup of your profiles on each site and NOT your computer itself.