There's probably still time to enroll in these courses for this spring semester in some colleges.  Others are already well into the spring semester and may not have openings or enrollment allowed at this point.  Sometimes students take courses in the summer to satisfy pre-reqs.  Some M.Arch programs are even pretty lenient about pre-reqs and will allow students to take them in their first semester (concurrent with the rest of the course load, which can be difficult.)  Some programs are stricter about pre-reqs and will require that you defer admission for a year, or even reapply, if you don't pass them beforehand.  Check directly with the school about their stand on this.

Yes Calculus 1, or equivalent is what is usually required - but if you've found something more introductory then check directly with the M.Arch program to find out whether it's acceptable. 

As for whether it should be hard to pass:  no, not particularly - but it depends on your comfort level with math.