Which account type are you using? A pst-file indicates a POP3 account but an
ost-file indicates an Exchange account.
Considering that you are now using a pst-file;
1) File-> New-> Outlook Data File
2) Then move all your data from the old pst-file to the newly created one.
3) Once you've done that go to File-> Data File Management and set the newly
created pst-file as the default.

Signature
Robert Sparnaaij [MVP-Outlook]
Coauthor, Configuring Microsoft Outlook 2003
http://www.howto-outlook.com/
Outlook FAQ, HowTo, Downloads, Add-Ins and more
http://www.msoutlook.info/
Real World Questions, Real World Answers
-----
> Issue:
> Just installed Office 2007 Professional atop Office 2000/Outlook 2002
[quoted text clipped - 19 lines]
>
> What should I do first?
purpleplume - 19 Dec 2007 20:42 GMT
Robert, I have POP3. That doesn't sound too hard. I can do that.
I think I have two PSTs actually, but the same process would apply to
both PSTs, correct? I realize there can be only one default. No
worries there.
Roady [MVP] - 22 Dec 2007 11:00 GMT
Yes, it works for either pst-file.

Signature
Robert Sparnaaij [MVP-Outlook]
Coauthor, Configuring Microsoft Outlook 2003
http://www.howto-outlook.com/
Outlook FAQ, HowTo, Downloads, Add-Ins and more
http://www.msoutlook.info/
Real World Questions, Real World Answers
-----
> Robert, I have POP3. That doesn't sound too hard. I can do that.
>
> I think I have two PSTs actually, but the same process would apply to
> both PSTs, correct? I realize there can be only one default. No
> worries there.