Paths to images

I am having trouble figuring out the "right" way to specify the path
to an image when it is an attribute of something other than an image
tag.

For example, I see that image_tag("myimage.png") automatically knows
to look in the public/images directory.

How do I accomplish the same thing for other tags? For example, my
layout has:

<td background="menu_bg.gif" width="1">

Also, in my css file:

tr#logobar { background-image:url("logo_bg.gif") }

In these cases it seems that specifying the image name is not enough.

First, I tried a relative path ("images/logo_bg.gif") but this failed.

A full path worked ("/images/logo_bg.gif") worked, but this causes
problems for deployment.

My server has the application root in a subdirectory. In other words,
my application is in:

http://my.server.com/myapp

All of the places where I had "/images/logo_bg.gif" fail on the
server. I have to manually change them to "/myapp/logo_bg.gif" for
them to work.

It doesn't seem like manually updating those links every time I want
to deploy a new version is the right way to do this.

What am I missing here?

Thanks for the advice. I did as you suggested and everything appears
to work fine.

FYI to any other newbies out there like me -- be sure to budget as
much time for deploying from your development machine to your
production machine as you spent writing your application (more, if
your application is pretty simple).

I suspect that this is a one-time problem. Once I get my first app up-
and-running I suspect deploying additional apps will be easy.