New to this, please help

My wife makes high-end window fashions (curtains, drapes, swags, jabot - I know, wrong forum). We both have technical backgrounds but little experience with programming.

We have typical Windows XP systems (latest updates), running MS-Office 2003.

The question and issues are:

She has developed several equations in Excel that can automatically figure out dimensions, cuts, and details for fabricating these window fashions (there is a lot of calculating to be done based on size, dimensions, patterns, style, and such).

She has let a couple of friends/peers use the equations and they love them. Word is gettig out that it is very good to excellent and that she could sell them as a prepackaged template.

I'm not sure were to go next, it is a moderate sized market (hundreds to maybe a thousand workshops) and it would not be a high-cost ticket to purchase, but potentially large enough to be cumbersome for us.

We would like to build an application or program that an end-user could utilize but not have access to the source equation or give away free or change contents. There would be 3-5 different calculations that a end-user could use, plus a reference library of tips and tricks that could be looked up.

I know there are several options for us (VB.net, Flash, Java, Just Basic, Ruby all appear to be options to us) but we have not been down this route ever.

1. Is this the correct way to go?
2. What would be the best application to use (pros/cons)?
3. Are we better off hiring someone (contract) to do this development? What might be the cost of this?
4. Is CD distribution the best method or are there other ways? (I guess a user could download or have it emailed if it wasn't too big).
5. What functional problems might we look out for in a mixed user population (various levels of Windows knowledge as well as varying Windows versions)?

Thanks,

Todd