This is Not A problem At all. If you have Installed Ubuntu Along With Windows,
Windows Xp: boot with windows xp cd,
go to repair screen,
choose your Windows and then Type fixmbr
and
fixboot
then Reboot
Windows 7 And Vista
boot with windows cd,
After The Language Selection ,Click Repair Your Computer.
Select Command Prompt and enter
bootrec /fixboot
bootrec /fixmbr
and restart..
now You can Use Ubuntu,Windows Etc
This is Not A problem At all.
If you have Installed Ubuntu Along With Windows,
Windows Xp:
boot with windows xp cd,
go to repair screen,
choose your Windows and then Type
fixmbr
and
fixboot
then Reboot
Windows 7 And Vista
boot with windows cd,
After The Language Selection ,Click Repair Your Computer.
Select Command Prompt and enter
bootrec /fixboot
bootrec /fixmbr
and restart..
now You can Use Ubuntu,Windows Etc