Hi.

Oracle is almost identical on all platforms. I've worked with NT/2000, HP-UX, Solaris and Linux and it's practially the same on all of them.

I would suggest you start on NT/2000 since you'll already have a good understanding of the OS. Once your Oracle skills have picked up a bit you might want to try Linux. It's about as close as you'll get to the big UNIX stuff without paying a fortune.

The amount of UNIX knowledge you need varies depending on the company. Some companies have UNIX system administrators so all you need to know is how to copy and move files etc. Others rely on the DBA to know loads of system admin stuff. The more you know the better, but you can get by with "UNIX for dummies" in some companies The OS specific manuals will tell you most of what you need to know for installation and performance tuning of specific platforms so it's not too bad.

Oracle is significantly more tricky than SQL Server. Try not to get stuck in the "This is bullsh*t, it's so much easier in SQL Server!" frame of mind. The truth of it is that Oracle is a pain in the ass compared to SQL Server, but that complexity allows it to do some pretty cool stuff.

It's a good idea to have some experience of a few different engines these days. We've got SQL Server and Access here as well as Oracle. You'd be surprised how many times I get asked questions about Access and SQL Server that start with, "Your a DBA so you should know this!"

Good luck