Inquiry Cart

Please look in the wiki, under the customer topic, at the custom fields that may be associated with such a customer.  Those values are stored at the customer level.

 

Then look at the product options topic, and note that you can define a field that will appear on the product page and prompty for an entry.  Those values are stored at the order line item value.

Again, you can model examples of these fields in the demo store.

If you require something that is outside of those features, then you are looking at custom programming.  As an example, you could look at www.tastefulgarden.com for an example of handling a requested delivery date.  Place any item in the cart and head for checkout.  You cannot get past viewcart.asp without selecting your preferred shipping date.  There are other ways that we have tackled this including simply inputting a date with a JS calendar module.  We used to have it that way in this site until the merchant asked for the current approach to be implemented.