First of all, welcome to linux!
Adding the USB and firewire drives won't be a problem. When you plug the drive in, take a look at the output from the dmesg command. On some distros you need to be root to use dmesg. All it will tell you is what the hardware address of the USB or firewire drives is. Chances are good if your machine has IDE drives, then the external drives will be /dev/sda1 or /dev/sda2. Dmesg will tell you where they are. If you have sata drives already in the case, then the external drives will be some letters down. With 1 sata drive in the case, then the externals will become /dev/sdb, 2 satas then the externals are /dev/sdc, so forth and so on. Once the hardware is found, you would mount the drive to a location within the file tree. Might be /mnt/usb and /mnt/firewire, or you might mount it within your home directory, all depends on how you want to do it. There are countless posts here asking about mounting external drives, so search that up. It is also quite possible that Ubuntu will automatically mount these drives, taking all the work away from you and making it automatic. If the drives are formatted with NTFS filesystem, then you can mount them read only, as writing to NTFS is still experimental. Copy the data off, format the drive, to anything else, then copy it back on. They are probably formatted Fat32, which linux can read and write to.
As for windows programs, check out the equivalency list here on LQ - http://wiki.linuxquestions.org/wiki/...ndows_software
If you have to use the actual windows program and not the equivalent, you'll need to use a program called wine, cedega, or crossover office. I haven't used any of them, but may people here use them with mixed results.
I have never used a TV tuner, but I suspect it would be automatically detected during installation, and would just require some software to work.