Can i use 64 bit ubuntu with 32 bit vista?

Try using the live CD to see if things run smoothly... it is the safest option for now.

Yes you can use 64bit Ubuntu, i assume so anyway, because they are both independent Operating Systems, unless you install using the Wubi which is just designed to be a temporary way of installing Ubuntu (although some people manage to keep it balancing on top of Windows for years). The 32bit version of Ubuntu is usually better tho. Either way here's the best way to install Ubuntu as a dual-boot so that you combine the strengths of both OS's rather than their weaknesses

https://help.ubuntu.com/community/BootFromCD
https://help.ubuntu.com/community/WindowsDualBoot

Good luck and regards from
Tom :)

Err, robos plan is always good as a first step before any install of almost any distro. It helps see if things work easily, flags up rare but potential hardware issues and is great to see if your internet connection gets picked up easily. Later if you ever run into troubles it's good to know you can always use the LiveCd to help deal with the issues involved.

To run a LiveCd session simply place the installer Cd in the cd/dvd-drive and reboot the machine. This should get you to a menu with "Try Ubuntu without changes to the machine", if not then this guide helps
https://help.ubuntu.com/community/BootFromCD
this default option (most distros don't give it a fancy title but do also have it as the default option) should get you to a working desktop, which we call a LiveCd session (if it works)

I am assuming that you are using a desktop version of Ubuntu as a server version does the same but gets to a working comand-line as server editions avoid the security issues of running a desktop-gui. I'm not talking about security in terms of malware because pretty much all linux distros are almost entirely safe from malware anyway :)

Good luck and regards form
Tom :)