你说“先装vista,后装xp...再修改bootrecord,但是x64 boot不了”，那是你安装的顺序颠倒了，微软关于Dual Boot有这样一段话：
To resolve this problem, install the earlier version of Windows on the primary boot partition, and then install Windows Vista on a new partition. If you want to be able to start from more than one operating system, install the earliest version of Windows first, and then install the later versions in the order of release. For example, install the operating systems in the following order:
1. Windows 2000
2. Windows XP
3. Windows Server 2003
4. Windows Vista
Install each operating system according to the standard installation procedure.
Note Install each version in its own partition.
如果一定要先装Vista的话，可以参见下面给方法：
http://support.microsoft.com/kb/933179
http://support.microsoft.com/kb/555852
Good Luck！