SELECT DISTINCT a.*, b.finditHere
FROM (tableA a INNER JOIN
tableB b ON a.fieldSP = b.fieldSP) INNER JOIN
tableC c ON b.finditinhere Like "*" & c.text2find & "*"
Access likes to see those parentheses in the FROM clause when joining >2 tables; in SQL Server you can omit them.
And yes, it is legal to use expressions other than "=", including functions, in a join expression, but be aware that doing so with large tables can lead to slow performance.