Windows Update Agent Client Version Numbers and Sources

v5.4.3628.1 - Windows 2000 SP3

v5.4.3630.11 - wuau22.msi

v5.4.3630.1106 - Windows XP SP1

v5.4.3630.2554 - Windows 2000 SP4

v5.4.3790.2180 - Windows XP SP2

v5.4.3790.2182 - Windows XP SP2

v5.7.0.2177 - WUS beta

v5.7.3790.1830 - Windows 2003 SP1

v5.8.0.2339 - WSUS RC1

v5.8.0.2469 - WSUS RTM

According to the WSUS Wiki site, the client must be at build v5.4.3790.1000 in order to be considered "WUA"