You could use an extra where clause to exclude certain servers based on their names, IP, domain, etc.
Where tblAssets.AssetName Not Like '%citrix%' And Cast(tblDiskdrives.Size /
1024 / 1024 / 1024 As numeric) <> 0 And Ceiling(tblDiskdrives.Freespace /
(Case tblDiskdrives.Size When 0 Then 1 Else tblDiskdrives.Size
End) * 100) < 10 And tblState.Statename = 'Active' And
tblDomainroles.Domainrolename In ('Stand-alone server', 'Member server',
'Primary domain controller', 'Backup domain controller') And
Case tblDiskdrives.DriveType When 3 Then 'Local Disk' End = 'Local Disk'
Where tsysOS.OSname Not Like 'Win 2003%' And Cast(tblDiskdrives.Size /
1024 / 1024 / 1024 As numeric) <> 0 And Ceiling(tblDiskdrives.Freespace /
(Case tblDiskdrives.Size When 0 Then 1 Else tblDiskdrives.Size
End) * 100) < 10 And tblState.Statename = 'Active' And
tblDomainroles.Domainrolename In ('Stand-alone server', 'Member server',
'Primary domain controller', 'Backup domain controller') And
Case tblDiskdrives.DriveType When 3 Then 'Local Disk' End = 'Local Disk'