Question : SSL on OWA--Which server?

I was trying to secure our Exchange web access but I had some questions. I currently have 2 Exchange 2003 servers with 50 users (1remote) and a dedicated OWA server with no Mailboxes, all located internally within our LAN. Here is what I did so far,

1. I generated a (CSR) file from our OWA server and sent it to an internet CA authority, then when I received the files,
2. I installed Certificate Services (from Add/Remove programs) on the OWA server
3. I tried to go to IIS/Default WebSite/Directory Security/Server Certificate/Process the pending request and install the certificate
However it is looking for .cer files when the files I received from the Certificate providers contain 4 files all with a .crt extensions. Am I missing a step? Here are the files I got

AddTrustExternalCARoot.crt
NetworkSolutions_CA.crt
UTNAddTrustServer_CA.crt
WWW.MAIL.MYCOMPANY.ORG.crt

Also was I supposed to install the Certificate services before I generated a CRT file on the OWA server?

AND THE MOST IMPORTANT QUESTION, Which server do I install this certificate on> The Back end server or the Front end server??

 Thank you very much in advance.

Answer : SSL on OWA--Which server?

You can convert your crt file to cer file. Here's how
https://support.comodo.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=808

You will install the cert on your owa server (front end)