Question Nr. 1
You mean the ConfigMgr Client?!?
Create a query with the following sql query:
select Name, ClientVersion, ResourceDomainORWorkgroup, LastLogonUserDomain, LastLogonUserName, ADSiteName, IPAddresses, ResourceId, ResourceType from SMS_R_System where Client = 1 and ClientVersion > "4.00"
Question Nr. 2
ConfigMgr Console --> Site Database --> Site Management --> right click your site + Properties
Then check in the internet for the version which is listed.
For RTM, it is 4.00.5931.0000
For SP1, it is 4.00.6221.1000
Question Nr. 3
On the Client goto Control Panel -> ConfigMgr Properties -> Tab General -> Configmgr Clientversion