How to install GRUB2 in USB driver

[李季]

 Hi, guys.
     This is my first email sent to the 'ubuntu-users' maillist. I have encountered a problem in installing GRUB in my portable USB.
I just want the GRUB stand alone in USB. However, the dual OSs (include Windows XP professional and Ubuntu 12.04 LTS) stand
two partitions on a only hard driver. If I plug in my USB. I wish to boot the Ubuntu 12.04 on D: diver (for example), but not to read the
hd MBR. I want to know whether it can be implemented or not.  Also, I have read some tutorial on Internet, It seems that letting alone
GRUB in USB  is OK. but I followed the steps, I failed. So if you can give me a detailed tutorial, it preferred. Of course, give me some
information is good. THANK YOU in advance.  Please ignore my poor English. and I wish the question is described clear. 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.ubuntu.com/archives/ubuntu-users/attachments/20131031/bbda481e/attachment.html>