Just installed 1557 (have not compared against 1555) using VS2005 SP1 on XP SP2 and created a managed C++ library project (File/New Project/Visual C++/CLR/Class Library) and the IDE becomes extremely unresponsive (2-3 seconds between keystrokes or just switching files). However, larger (400k lines) C# and (150k lines) pure C++ projects work just fine with no slowdown.
*um* that does not sound right at all. Your reference to large files in the first post left me with the impression you had imported a large file into this new project.
Can you try stopping VAX from loading at all, as described here, and see if this makes any difference?