Using a Microsoft SCCM Web Report (SQL query), Dell models and corresponding BIOS revisions in your environment can be determined. This report can be helpful for gauging the scope of your targets:

SELECT CompSys.Manufacturer0 as ‘OEM’, CompSys.model0 as ‘Model’,BIOS.SMBIOSBIOSVERSION0 as ‘BIOSVersion’, COUNT(Sys.Resourceid) AS ‘TotalSystems’
FROM V_R_System as Sys
LEFT JOIN V_GS_PC_BIOS as BIOS on Sys.resourceid = BIOS.resourceid
LEFT JOIN V_GS_COMPUTER_SYSTEM as CompSys on Sys.resourceid = CompSys.resourceid
WHERE

CompSys.Manufacturer0 LIKE ‘%dell%’
AND (CompSys.Model0 LIKE ‘%optiplex%’
OR CompSys.Model0 LIKE ‘%latitude%’
OR CompSys.Model0 LIKE ‘%precision%’)

GROUP BY CompSys.Manufacturer0,CompSys.model0, BIOS.SMBIOSBIOSVersion0
ORDER BY CompSys.Model0, BIOS.SMBIOSBIOSVersion0

Reference: http://www.delltechcenter.com/page/Dell+BIOS+Upgrades+for+Enterprise+Clients+with+Microsoft+System+Center+Configuration+Manager+2007