How can I tell which version of Exchange I'm running.

There is a high ram usage by store.exe. I searched on web about the solution and found that there is a patch that fix the problem and reduce the usage of store.exe. But for that I want to find out which version of Exchange I am running. The patch that I had download supports Exchange 2003. I am not sure what I am using. It may be Exchange 200 also. I went inside the System Manager where I found About Exchange and on that it was mentioned some :6.5.6944.0. Should I apply the patch.

As per the version number that you had mentioned (6.5) you are using Exchange 2003. So you can simply apply the patch. You can also run Windows update and that is a safest way to find out critical updates. Now it looks that store.exe is consuming a high ram due to some automated process. You have to check some more application which are associated with store.exe and stop them. It would help you more in facing the issue.

Go for the patch. But also check the requirement. Some patches does not work well for SP1 or SP2 version. It is a bit frustrating to work on issue with Exchange. I had wasted a long time on similar issue while I was using Windows Server 2003. There was a hotfix which I installed blindly and landed on error 51. There was no problem with the data but somehow it affected the functionality. Things were restored after I removed the patch.

No one here is talking about store.exe ram usage. I am linking a blog below that has more detailed information. This can help you to find out why store.exe is so much ram consuming. And some tips to enhance the performance of server. Before installing any patch you must go through the article one time and then you can find more ways of troubleshooting the issue.

Why is Exchange Store.exe so RAM hungry?

It is a very common bug with Exchange. It really affects the performance to great extent. The higher number of mailboxes the more RAM will be utilized. As per microsoft around 5MB of ram must be allotted to each mailbox and it would work better. Microsoft has a storage calculator that help you to find out the requirement more easily based on the users and their usage profile.