Stop making excuses and do yourself and your staff a huge favor by upgrading (or implementing for the first time) your law office technology.
Most small law firms pay insufficient attention to backing up their critical data. Those that have backup systems often rely on mechanical tape backup systems that require far too much user invention and are inherently unreliable. The better solution is a fully-automated on-line backup.
If your computer is more than 2 years old, it probably does not make sense to upgrade it. You would do better to replace it and (after cleaning off all firm and client related data) take it home, send it home with an employee, or donate it. The price of a new computer with a fast processor, a large hard drive, plenty of memory (RAM), and the Windows XP operating system is not much more that the cost of most upgrades.