For Spring 2011, CSE 457 will have a prerequisite of CSE 303 or 351 and 326 or 332. Math 308 is recommended. In the future 333 will still most likely be the required prerequisite, so if you plan to take 457 in fall, take 333 in spring.
This spring there is an exception since 333 is not being offered until spring quarter.
Here is the link to the rest of the new prerequisite courses: http://www.cs.washington.edu/education/ugrad/current/CSE_prereqs.html
CSE Advising