You can download NetBeans 4.1 RC1 here
Final release will differ only slightly from Release Candidate 1. I recommend to upgrade to everybody who is using NetBeans 4.1 EA, EA2, beta, q-build or daily build, RC1 is definitely more stable. For users who prefer final releases: you probably want to wait till 4.1 final which will come in May. On the other hand if you have some issues with 4.0, you could try 4.1 RC1 if they were solved, there was a huge amount of bugfixes - see table below.