Only you can answer that.
5GB of downloads is a large amount, especially if you only use the internet for email, surfing web sites, chatting, etc. It should be plenty. Here's some basic comparisons;
1000 KB = 1 MB
1000 MB = 1 GB
1000 GB = 1 TB
KB: Kilobyte (you may also see kilobyte as just k)
A typical web page, including its graphics should not exceed 100KB, (whilst that may have been true a few years ago, many web sites nowadays have more content to make it more appealing to visitors, but even so, web site content including graphics is not very large).
If you are downloading files like software, music, videos, etc to your hard disk, (beware of copyright and pirating issues here with file-sharing sites), then those files individually will be larger, but even so, the average size of a typical music file will be around 2 to 4 MB, and so with 5GB that would be a very large number of music tracks each month. (4MB x 250 files = 1GB. x 5 = 1250 music files). Software and video files will be larger, depending on individual files.
ISPs, (Internet Service Providers), are now typically imposing limits on downloads because of the growth of broadband availability and the number of users downloading music and videos. The limit, or cap, is to help manage excessive use of the connection's bandwidth by some, which creates bottlenecks and restricts bandwidth for others.
The choice is yours here. If you do not feel that $60 a month is a reasonable expense for your internet connection then shop around.
I am thinkng about those $60/month 5Gb deals with wireless.
But don't know how much GBs on Internet do I use per month.
Is that info available on WinXP?
Or is there software that can tell me that?