Do you actually have a museum that is open to the public (or by appointment)? Or do you have some other way that you operate in the public interest? Or is that not required to qualify as a 501(c)3? I just looked it up with Google: (3) Corporations, and any community chest, fund, or foundation, organized and operated exclusively for religious, charitable, scientific, testing for public safety, literary, or educational purposes, or to foster national or international amateur sports competition (but only if no part of its activities involve the provision of athletic facilities or equipment), or for the prevention of cruelty to children or animals, no part of the net earnings of which inures to the benefit of any private shareholder or individual, no substantial part of the activities of which is carrying on propaganda, or otherwise attempting, to influence legislation (except as otherwise provided in subsection (h)), and which does not participate in, or intervene in (including the publishing or distributing of statements), any political campaign on behalf of (or in opposition to) any candidate for public office. (4) (A) Civic leagues or organizations not organized for profit but operated exclusively for the promotion of social welfare, or local associations of employees, the membership of which is limited to the employees of a designated person or persons in a particular municipality, and the net earnings of which are devoted exclusively to charitable, educational, or recreational purposes. (B) Subparagraph (A) shall not apply to an entity unless no part of the net earnings of such entity inures to the benefit of any private shareholder or individual. I can see where a computer museum falls under "educational purposes" in 501(c)3, if it is accessible to the public, but not how it would qualify for 501(c)4. But of course, IANAL.

In the second warehouse I have office space that is enclosed that I setup as small museum area that can be shown by appointment and before I filled the warehouse I could give a small group(2 to 3 people) tours of the warehouse (no insurance to cover large groups). I used to give presentations at the local middle and high schools in the TwinCities (MN). My needs right now are for a permanent place for the collection (rents went up again) and to get some funding to help with the expenses. If I meet these two goals then I will be able to open to the public with regular hours.