A monitor usually far outlasts the computer, so it is well worth investing in a good monitor for the years that you will be staring at it. As long as your video card has at least 1 mb RAM then you can set your resolution to 800 x 600 at 16 bit colour for pleasing results. You are not using Netscape as your browser. Lifesite is designed to Netscape standards although much of LifeSite can be viewed well in Internet Explorer. If you don't have Netscape, it is a simple matter to download it free from Netscape and install it.
Most people have more than one browser on their computer.
Your telephone line needs repair. Yes, this is a common cause of internet problems. The fact that you aren't having problems with your voice calls doesn't tell you anything about the quality of the line for Internet data transmissions. It's time to call Bell or whoever provides your line, explain the problem and insist that they test your line. You must insist because they usually don't like doing this.