avast is fine. spybot is the safest free software probably on planet earth! its a great tool, but doesnt remove everything. there isnt a software for this out there that removes all threats. you need to use multiple. but spybot will let you know if the threats exist.
any linkys router will be fine. make sure to use the cd it comes with when you set it up.it needs to work with the modem. you are correct about the switch. in laymans terms its a ethernet extension cord. a router has a switching device in it, but also gives out addresses.
using to not using a router. think of it like this:
2 scenarios:
1) you have a letter, you mail it to yenim who lives in building a. apartment 1.
you write the address on the envelope, and the mailman brings it to the building. he has access to the mailboxes and puts each persons mail into the mailbox os said receiver.
or the same story but:
2) you have a letter, you mail it to yenim who lives in building a. you have no idea its an apartment building.
you write the address on the envelope, and the mailman brings it to the building. he has no access to the mailboxesand has no clue who lives where. he gives the mail to teh dorrman who gives it to the mailroom, who depending on the name, pputs it in peoples mailboxes.
the first is using the internet without a router, the second is with. without the router, the outside world (filled with hackers, crackers, viruses, spyware, etc) has direct acces to you machine. with a router, the router asks the packet (how information travels in the world wide web)where it needs to go, and then directs it if it is sent directly to the machine that asked for it. otherwise the packet is rejected, and it moves on down the road to teh next modem that is unprotected.