For DX the diff between 2003 and 2005 will be next to nothing. The only thing that might flag a warning is if you use the C standard library functions which Microsoft has taken it upon themselves to declare deprecated - which it IS NOT DEPRECATED and is still part of the ISO standard.
To remove deprecation use _CRT_SECURE_NO_DEPRECATE in your project options under pre-processor. This will remove those non-standard warnings. Again the only thing non-standard and deprecated here is MS's attempt to hijack the language.
