I'd recommend that you study the CCNA Routing & Switching certification from Cisco to start with:
ICND1/2 goes into a lot more detail than the composite exam btw.
If you don't have any previous experience of networking, it won't really matter what certifications you do hold, so I wouldn't worry about it too much. The most important thing, at least to start with, is understanding (fundamentally) how networks work. If I was interviewing you, certificate or not, I'd still ask the same questions. :)
There are other network certifications you can take, but the CCNA not only teaches you about networking, but also how to administrate Cisco networks which practically every company in the world will use to some degree.
The amount of time it takes depends on your aptitude really, but that certificate will open a lot of doors for you so it is worth sticking with. If you have the time, a few hours a day studying should see you clear the exam in a couple of months.
Salary wise, entry level networking is (depending on your part of the world) roughly £25,000 p.a. CCNA plus 1/2 years worth of experience is normally around £35,000p.a. Once you have a few more years of experience (or if you have a gift for it like me :), even less) and some more certs, you won't have any problems finding work that pays really, really well.
If you need any more help or have any more questions, just let me know.
Best of luck.