virus removal for my customers

Yes, you're on the right track.
You do need a good antivirus software and both Symantec and McAfee are among the best antivirus software manufacturers. When you buy a licence, you usualy buy a right to upgrade to a new version of software (usualy for 1 or 2 years). This is important because even though you can get new virus definitions downloads for free, the manufacturers sometimes release completely new products to support new technologies (like new Windows, Exchange, Web Servers, Firewalls etc).
So, how would you support customers?
Plan A (preferred) - Sell them AV software and install it on their machines.
Plan B - If they come with a suspect machine, you may offer to scan it for them. You can do it in 3 ways:
1. Remove their diskand scan it in your known good system
2. Boot their system with a boot floppy or boot CD. Most AV SW has an option to create such disks (but you will probably have to supply operating system like Windows 98).
3. Over the network. Install network card in suspect system, enable file sharing and connect to the shared network drive from your known good system.

One more point. It is important to scan e-mail too. You can do it by importing mail files to your known good system or by installing AVSW on your customer's system. But beware of the licencing issues that may arise from this scenario.