Helping people with computers... one answer at a time.
When you install a program, quite often one of the questions it will ask you is whether you want to install for the current user only, or for all users.
In other words, exactly what you're asking about.
The question is what if the setup doesn't ask, or what if you selected "current user only" ... can you still use the software when signed into a different user account?
Unfortunately, it's that all too common answer:
Let's look at some of the possibilities.
The difference between installing for all users and installing for the current user only typically boils down to where the setup program places the shortcuts for the program, where it places any directories or support files, and possibly where within the registry it places program settings. It all depends on the specific program being installed (hence the "maybe"), and some programs will have more differences, and some will have fewer.
For example, if you take a look at "c:\documents and settings" on your Windows XP installation, you'll see at least two directories: one with your user name, and one with the name "All Users". Dig a little deeper, and you'll see a "Start Menu" item beneath each of those. The start menu you see is the result of Windows displaying the contents of both of those: the contents of "c:\documents and settings\all users\start menu" and "c:\documents and settings\--your user name--\start menu" are merged and displayed as the system start menu. So if a program's shortcut appears in the "all users" portion, then it'll show up for everyone. If it's only in one specific user name, then only that user will see the shortcut. Similar, though not identical, concepts apply to the registry and other items in within "documents and settings".
The point of all that is that when a program is installed, it needs to decide where to put its information: either in "all users", or in a user specific section. Sometimes it asks, sometimes it assumes, and sometimes it assumes wrong.
So, what to do? If you're logged in as user "A", and want to access programs that are only visible to user "B", here are some ideas to try:
Unfortunately, these ideas will not work for all programs. For example, manually creating or copying a shortcut may bypass additional setup steps that some applications require.
The reason that there's no blanket answer is that setting up an application can be fairly complex, and it really is up to the manufacturers of the specific applications to "do the right thing". Not only is "the right thing" subject to interpretation, many don't do it even when it is clear. So a final suggestion is, of course, to contact the manufacturer of the package you're having issues with and ask if they have a recommended approach to the issue.