IRS Publication 550 (re. Nov. 87), "Investment Income and
Expenses," is currently available at IRS offices.  Pages 16-17
deal with investment clubs, whether corporations, associations,
partnerships, or partnerships which choose not to be treated as
a partnership, which is probably the largest category of clubs.
The information below on this last choice is quoted from IRS Pub
550 (beging quote):
    Choice not to be treated as a partnership.  An unicorporated
    club used only for investment purposes, and not for the
    active conduct of a business, is not treated as a partnership
    if it so chooses.
    To make this choice, the club must file a partnership
    return, Form 1065, for the first year for which it does not
    want to be treated as a parternship.  The return must be
    filed by the due date, including extensions, for filing the
    return.  This return should show only the name or other
    identification and the address of the club.  A separate
    statement must be attached to the return showing the
    following information:
    1) The names, address, and identification numbers of all the
    members of the club,
    2) A statement that the club is used for investment purposes
    only and that its members can figure their income without
    figuring partnership taxable income;
    3) A statement that the club is an investing partnership,
    4) Inforamtion about where the terms of the agreement,
    written or oral, under which the club operates, may be
    obtained, and,
    5) A statement that all the members of the club have chosen
    the exclusion from partership treatment.

    If the investment club makes this choice, From 1065 need not
    be filed for later years, but the members must report their
    share of income, deductions, and credits on their individual
    Forms 1040.  The members may deduct their share of investment
    expenses, subject to the 2% limit, on Schedule A (Form 1040)
    if they itemize their deductions.  The choice remains in
    effect as long as the club qualifies or until the
    Commissioner of Internatl Revnue approves its application to
    change the choice.  (End quote.)

Note that each club must apply for and get its own employer
identification number even though it chooses not to be treated
as a partnership.  Appliation for EIN numbers are made on IRS
Form SS-4, "Appliation for Employer Identification Number."