1251 Alg is complex numbers, vectors spaces, linear transformations and eigenvalues. You'll need all the stuff about matrices and solving systems of equations for the last three of those.
1251 Calc is integration, differential equations, sequences and series, several variable calc. It builds on the calculus you've done, although some of it could have been done without 1151 if you did ext 2. The differential equations is mainly just learning some algorithms but there is some abstract stuff that uses vector spaces and linear transformations. Some of the series stuff (like does 1+1/2+1/3+1/4+... converge) is like the improper integrals stuff (eg does int(1/x,x=1..infinity) converge?).