2005 will back save to 2000 based products. Ask your drawing supplier to always give you drawings in this format. Easy for them as a batch converter is included with 2005. Alternatively yes you could buy 1 copy & DIY.
Brenda is spot on though if you did a Return on Investment analysis you would perhaps see that the new features since 98 could make an increase in productivity which would give payback over a short period. Talk to me privately for a help with ROI - I will be out the office until 26/7 though.
Note - and here is one I've used previously to convince thrifty employers - Autodesk remove support & upgrade cost benifits periodically down the chain - every 4 years or so. Thus you can no longer upgrade your 98 or 2000i - need to buy a new product (more cost). It is always beneficial to stay within the upgrade loop - even if you miss one or two try to upgrade before your release is unsupported. If you can afford it & can prove the benefits - cheaper in the long run.
If in the US go subscription & that way you are always up with the game & have an annual cost you can budget for.