Where do 'W2k' and 'NT4' go tomorrow?
Well, it's not so much about tommorrow ! but its 'final destination' :) NT 4.0 was released in 1996 while W2k in year 2000. The official end of support life for Windows NT 4.0 is 31st Dec 2004. There won't be any FREE support after that, you need to pay ! this is a new 2 years custom support agreement for NT 4.0 customers. On the other hand, there will not be SP5 for W2k, instead W2k customers will get a rollup update. Hmm... consider the end of support life for W2k is around 2010, we have 5 more years to go..... how many rollup update(s) we will get ?
Anyway, you should be at least running on W2k or W2k3 :) or best OSS based? Now, here's few links about Microsoft product life cycle and it's support policy.
1. Locate Your Product (either by product family or name)
2. Product Lifecycle Dates - Windows Product Family
3. Microsoft Support Lifecycle Policy FAQ