Ubuntu has already fixed bug & respun ISO, which was causing ubntu dual boot error. Meaning if you already have XP / Win7 installed and after upgrading from 9.10 to 10.04 you might not find Grub entry for MS OS.
By any chance if you have downloaded 10.04 iso before release, you might find dual boot error after installation. To fix you can use ubuntu recovery mode and regenerate Grub entry.
Reboot your PC.
goto ubuntu recovery mode
in recovery menu
select grub (Update grub bootloader)
reboot the system. All should be fixed.
