Can I reinstall IIS without interrupting other services?

What do you mean by other services?

The service I most want to keep running is SMTP. Are there any others that might be affected?

Reinstallling it should NOT cause problems for other services such as SMTP service, but it will have to shut down and restart the SMTP service, as well as FTP, NNTP, Exchange routing engine, WWW publishing service, and possibly a few more (depending on your setup).
Once the reinstall of iis is complete (probobly a couple of minutes) it will restart these services and you should be back up and running 100%.

Will it change the SMTP configuration?

no it will not

Just want to make doubly, triply sure, here.

Keep in mind that on an Exchange server, we have a bunch of virtual directories for the Exchange Virtual Server, such as Exadmin, Exchange, Microsoft-Server-ActiveSync, OMA, etc.

Are you saying that all of these will be recreated without having to reinstall Exchange?

Thanks.

In attempting to get Exchange ActiveSync working with a Treo 700w, I messed with a bunch of settings such as certificates and permissions. I didn't back up the entire configuration and now many things don't work.

Yes, stupid, I know.

I still have the initial backup from when I set up the server.

Can you recommenda fix for this particular situation?

THanks

I had major 700w issues when i started using them... what is the error you are getting on your treos?

Try resetting your authentication permissions for your virtual directories as shown here: http://www.msexchange.org/tutorials/Securing-Exchange-Server-2003-Outlook-Web-Access-Chapter5.html

Then if you use forms based authentication and ssl, you will prob. have to impliment this: http://support.microsoft.com/kb/817379/en-us

When that is done, make sure you've installed your servers certificate on your treos (if you use a self generated cert).