Solution to Project Euler #1 - multiples of 3 and 5
In Scheme, we use hyphens to separate words, not underscores. Also boolean-returning procedures should end in ?. So it should be multiple-of?
Instead of (equal? x 0), use (zero? x).
Instead of a recursive loop, you can use for comprehensions:

(for/sum ((i (in-range 1000))
          #:when (or (multiple-of? 5 i)
                     (multiple-of? 3 i)))
  i)


Surely, that's much more readable. In my humble opinion. :-)
Notwithstanding the last comment, your formatting for your primes procedure is not ideal. Here's a more proper formatting:

(define (primes current total)
  (if (&lt; current max)
      (primes (add1 current)
              (+ total (if (or (multiple-of? 5 current)
                               (multiple-of? 3 current))
                           current
                           0)))
      total))