You can flash the BIOS via windows which is easier than via DOS.
The latest version for the 530 on the Dell site is 1.0.18 dated 2009. For the 530b it is 1.0.2 dated 2009. (make sure you download the correct one for the machine)
Which BIOS version are you currently running? Should show you the BIOS number on the boot screen.
Download from here to your desktop: http://downloads.dell.com/bios/530_1018.EXE (530) or http://downloads.dell.com/bios/530b-102.EXE (530b/530Sb)
Follow these instructions:
Run the BIOS update utility from Windows environment
Double click the Icon on your desktop labeled 530_1018.EXE.The Update BIOS window appears
Click the Update button.The message Updating BIOS. Please DO NOT POWER OFF! appears. BIOS update will begin.
After BIOS update complete, the WinFlash window appears to tell you "Update successful". Click Yes button. The system will restart and the BIOS Flash will be completed.