Hi,
When you first start with VBA add-ins they can be extremely confusing - there's a steep learning curve involved.

(1)
When you install the add-in, this tells Excel that it should open the add-in. The add-in will automatically be opened when it is installed or when you launch Excel. This is expected behaviour. For Excel to run VBA code, the workbook that contains that VBA code must be open. The same applies to VBA add-ins. This however, should not be an issue for your end-users. If the ThisWorkbook.AddIn property of the add-in is set to true then all of the worksheets of the add-in will be hidden from the Excel UI. The fact that the add-in workbook is open will only be apparent in the VBA IDE. For clarity that the file is an add-in, you could save the add-in as an xlam file instead of an xlsm file.
The toolbar/menu customisation should be done dynamically by the add-in when it is opened. You can do this with VBA code in the Workbook_Open() or Workbook_AddinInstall() event handlers. It shouldn't be done in advance. When the add-in is unloaded, it should clean up after itself and remove the toolbar/menu customisations. This is done from the Workbook_BeforeClose() or Workbook_AddinUninstall() event handlers. This way, the toolbar/menu controls relating to your add-in will only be displayed when the add-in is installed, making it a user-friendly experience. Your profile says that you are using Excel 2003, but your add-in seems to have an Excel 2007+ format so I can't be more specific on this. Are you actually customising the ribbon with RibbonX?

(2)
I can't tell you what is wrong with your code unless you post the code (or attach the add-in) on the thread. I'd suggest you address the points I raised in (1) above and then let's see where we're at.
Once you've got your add-in working there are further considerations regarding deployment and updating. This is just a heads-up that once your add-in is working perfectly, We need to go through these deployment and updating issues before you distribute the add-in to your colleague(s).

Incidentally, you can also use Personal.xls / Personal.xlsm to have macros available across all of your Excel. But this would be personal to you.