Everything is a trade off. Size against price. It is a good idea to get a larger hard drive if you plan on adding a lot of software to your computer, or if you have a lot of personal files like MP3 music files and photographs. The average user can get by with a 8 to 10GB hard drive. Some people will never use more than 3 or 4GB. Then people who do a lot of graphic artwork or record a lot of MP3 music will use over 30GB.
Also consider that Windows 95/98/NT all use a .SWP file which is used as virtual memory so that a percentage of your hard drive will always be inaccessible to you. This space is usually very small (like 256MB). If you have a 15GB hard drive you will only show it being 13.6 GB in Windows. The reason for this is because the disk has a partition that uses some of the space as well as being formatted, which also uses some of the disk space. Also, some disk manufacturers measure a GB as exactly 1,000MB which is not "exactly" accurate. When the manufacturer measures space this way, a 15GB hard drive will be short by 24MB times 15 totaling 360MB short to begin with.
250 GB, if it's fast enough for your usage should be great. Good luck with your drive.