You're dealing with a pre-standard C++ library, and you've seen it won't compile with a standard compiler. You can always try the quick work-around by creating, say, iostream.h with the two lines #include <iostream> and using namespace std;, and that may work. It isn't reliable, and may cause hard-to-find bugs that will appear at an inconvenient time.
If this is a library from somewhere else, you could see if it's been updated.
The thing to realize is that the code isn't correct anymore. It may have been correct for some implementation at some time, but it isn't now. (Are you sure it was originally for gcc 3.0? Pre-standard compilers were, well, not standard, and had a lot of oddities. Avoiding that is what standards are for.) If you do install the original system, you may be unable to interface with the library properly, and new code isn't going to work. A library that doesn't interface with modern code is of limited use.
Otherwise, you're going to have to abandon the attitude that you can't change the library, and convert it to standard C++. There will likely be quite a few bugs that are fairly easy to fix (like the scope in for (int i = 0;...)), and may be some subtler problems. The code may have been correct for a certain compiler, but it isn't now.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
