Slow to open Excel document

Windows XP SP2 (+all latest updates)
Office 2000 (with all latest MS updates)
Excel document created in MS Office 2000

It takes about 15-20 minutes to open Excel document. After it finally opens, a message tells us that excel re-calculates all formulas in document prior to opening it as the document was created in previous version of excel when it wasn’t. After re-Saving As again-and-again in 2000 format, and closing the document, it still takes 15-20 minutes to open.
Document opens fine if Office 97 is used.
The problem occurs on any PC if office2k is used.
It doesn’t matter if document is on local or network drive.