You can create two queries and combine them in a Compound Query to find these donors.
In this Example, we'll be looking for all donors who only gave to the "ABC" fund.

First we'll create a query to find every one who gave to the ABC Fund.

1.Click the Queries button on the menu bar
2.Click Manage Queries
3.Select a category that you want to store this query in (Ex: Base)
4.Click New Query under the Tasks menu
5.Name the query Donors to the ____ Fund
6.Set the Starting Query to Base: All Constituents - A
7.Set the Data Return Type to Accounts
8.Select Match Each Criteria under the Criteria Matching field
9.Select Commonly Used Fields from the Browse Fields drop down menu
10.Select Individual Transaction Received from the list of links
11.Choose Greater Than Or Equal To .01
12.Select Funds from the list of links
13.Select the Fund you are looking for
14.Click Save And Preview

Next, we'll create a query to find every one who gave to funds other than the ABC Fund.

1.Click the Queries button on the menu bar
2.Click Manage Queries
3.Select a category that you want to store this query in (Ex: Base)
4.Click New Query under the Tasks menu
5.Name the query All Non ________ Fund Donors
6.Set the Starting Query to Base: All Constituents - A
7.Set the Data Return Type to Accounts
8.Select Match Each Criteria under the Criteria Matching field
9.Select Commonly Used Fields from the Browse Fields drop down menu
10.Select Individual Transaction Received from the list of links
11.Choose Greater Than Or Equal To .01
12.Select Funds from the list of links
13.Select the all of the OTHER funds (other than the one you are looking for)
14.Click Save And Preview

Finally, we'll create a Compound Query to eliminate the Accounts that have given to funds other than the ABC Funds.
 
1.Click the Queries button on the menu bar
2.Click Manage Queries
3.Select the Category where you would like to store your query
4.Under the Tasks Menu, Select New Compound Query
5.Name the Query Donors only to the _______ Fund
6.Set the Data Return Type to: Accounts
7.Intersect/Add or Subtract: Subtract
8.Category and Name, Query 1: Donors to the ____ Fund
9.Category and Name, Query 2: All Non ________ Fund Donors
10.Click Save And Preview