I've dealt with this one before. See the following 2 MS KB articles depending on your version. personally I went the route of converting to SQL 7 and then to 2000 rather then doing the patch as it was a one-shot deal.

Q279454 ACC97: "Overflow" Message When You Try to Upsize to SQL Server 2000
Q272384 ACC2000: "Overflow" Message When You Try to Upsize to SQL Server 2000