Two grub errors - dual boot and error 29

Hello

Ok, first of all I have successfully installed Ubuntu 7.04 onto an external hard drive. I also have my Windows XP installation on my internal hard drive. Sounds good the operating systems are there and working but there are two problems.

1. When I installed Ubuntu it did detect the Windows XP SP2 system but it did not offer this as an option in grub, so the dual boot is missing.

2. If I load Ubuntu from the current grub I get "error 29 disk write error press any key to continue". In order to load Ubuntu I have to edit the grub delete the last line which is savedefault and then boot. It boots fine but I have to do this every time I turn on my PC - a pain.

Can you anyone please help me put in the windows option and get rid of this error 29 problem?