Most of the apps that come with OSX are the best ones to use.

As for the PS/2 keyboard, there are PS/2-USB adapters all over the place.

Link

Is it just a firewall? If so, then I need more products like Anti-spy, Anti-spam?

If you don't have a habit of opening every shiny ad you see, chances are you won't ever have to deal with any spyware. Even if you do you'll probably be safe simply because most spyware isn't designed for the mac. That doesn't mean you should be utterly promiscuous when it comes to browsing, but being different can be useful.

But if you feel a great need for anti-spam and anti-spyware as well as a even easier firewall you could fork out 50 bucks a year for Norton. I have to say though your money would be better spent on practically anything else.

The built-in firewall isn't the easiest thing to understand, but once you understand what the buttons do (and that you're better off leaving an option unticked if you don't use it) you should be fairly secure. Just make sure to keep up to date with Software Update and you'll be fine.

I agree.  I have had no need for Toast since OS X burns any kind of cd I want with no problems.

AV - While there aren't many viruses out there for Mac yet, I generally load up Symantec AV on any box I'm worried about, Mac or Windows. Though it takes a lot of config work to get rid of annoying behaviors

Firewall - I use a combination of hardware firewall on my router and then the built-in firewall rules on the box. If you secure your router well enough, you don't need to worry quite so much about your box, especially if you're doing basic NAT on the router, attackers can't specifically target anything behind it.

CD Burning - The built-in OS burner functionality works great. Haven't needed anything else yet.

Mail - Mail.app is a great mail application (and comes with OS X). Sure it lacks all the widgets and gadgets that come in apps like Outlook, but it does mail exceedingly well. The rules, smart folders and spam filters are very well done and the interface is extremely clean and easy to use.

PS/2 Keyboard - While I'd generally suggest going for a newer USB keyboard, your PS/2 should work with a PS/2 -> USB converter. However, if you have any special programmable buttons (i.e. a web browser key etc), those will not work unless the manufacturer has OS X software available.

Be careful dismissing the risk of virii and spyware on a Mac. It's there, just quiet.

True. But it's nowhere near the risk of a PC. As long as you have the firewall switched on and are reasonably careful in what you do (just like you should be on any machine) you should be okay. The main cause behind viral outbreaks on the internet is human stupidity, not flaws in the hardware.

OSX just has the advantage that safe browsing is a little easier; it's got some useful immunities. You can get an STD (stupidity transmitted disease) but you have to try that little bit harder.

Thanks everybody for your respective comments.

Now I'm trying to convert my PS/2 keyboard to USB keyboard by a PS/2 (Female) to USB (Male) converter. The converter I've is a generic converter -

and can convert PS2 mouse to USB. But, I'm using Microsoft USB mouse. So, no such converter is needed. What I need is a PS/2 to USB converter for keyboard and I think the following one would serve my purpose-

Thanks Adamness for the link. I shall try the converter. If works, then it's OK. Otherwise, I've to agree with Zoomba who has suggested me to buy a new USB Keyboard for Mac. Then I can try all the software/utilities you've suggested.
Thanks Sir Zubaz for the link. I would go through the topic you've referred to. It's true that the graphical interface of Mac is probably the best. Hope virii won't like any pretty things like Mac!!!