In a previous post (Recovering GRUB After Installing Windows 7) I described a situation where GRUB would not be able to detect your Windows 7 boot partition after you installed Ubuntu. The fix was to point the root directory to a small (or secret?) partition outside of the main Windows 7 NTFS partition.
I recently demolished my Ubuntu partition and installed the latest Ubuntu 10.04 (Lucid Lynx), and it looks like the previous GRUB issues have been resolved. The installation went smoothly and the updated GRUB was able to install and boot into my Windows 7 partition with no problem.
It’s awesome when Ubunut just “works” 
One Comment
i have win7 on 1st drive and ubuntu on 2nd drive and when i boot the system first bootmgr get called and it contain two entry one is win7 &second is ubuntu ,when i click on ubuntu it call grub from it i get boot in ubuntu .
now i reinstall win7,after that it directly boot in win7 and i can not boot in ubuntu ,what shall i do get boot in ubuntu