I want to take a little detour and discuss the Greyhawk modifications to learning spells and how I would assign spells to new characters. Greyhawk is, of course, famous for expanding the uses of the six ability scores, including the addition of the effects of Intelligence on spells known. There's only a chance of knowing or being able to know any given spell, a minimum number of spells known, and a maximum number knowable. AD&D used a very similar table, but adjusted for the fact that low Int Magic-Users are no longer possible in AD&D.
Greyhawk doesn't give any instructions on applying the table, but the interpretation in AD&D is: when a Magic-User finds a spell and attempts to learn it, percentile dice are rolled to see if it's possible. If so, the PC can add the spell to their spellbook. Otherwise, the spell can't be learned. The exception is: if the M-U has tried to learn every spell on the list and hasn't met the minimum number of spells known. the player is allowed to check again for each unknown spell in their possession until they've met the minimum number. Once the PC has the maximum number of spells possible for that level, the M-U can't learn any new spells of that level.
Greyhawk doesn't say how to assign spells to a new Magic-User PC, but you could use the same technique at character creation, checking every spell on the standard list until the minimum number is met. That's a lot of die rolling, unless you're playing an Int 3 M-U. This method also involves a lot of paperwork; you need to keep track of every spell that's been checked.
In the AD&D DMG, there's a different method: all M-Us automatically know Read Magic and get one roll on each column of a special table that divides common 1st level spells into attacks, defenses, and miscellaneous. Thus, your M-U normally starts with four spells. Although that does give players incentive to search for spells they didn't get, it's a bit of a crock,since Read Magic has changed in importance; it's no longer a shortcut to allow immediate use of found scrolls, but is instead wasted space, a spell all M-Us must know whether they ever use it in play or not.
In Men & Magic, however, there is no restriction on spells knowable other than research expense. A lot of us use the rule that 1st level M-Us know all the standard 1st level spells at the start of the game, which avoids the die-rolling. I thought there was an explicit statement of this in M&M, but the last paragraph in the magic section only states that spell casters acquire spellbooks. There may have been an explicit statement in Holmes Basic or another book in the classic line.
One of the side effects of not using the Greyhawk/AD&D rule is that there's no chance of interpret the percentile die roll as a way of bypassing magical research, nor does a player ever max out their character's spell knowledge. Learning spells is only a matter of spending money, so players have an endless incentive to keep acquiring treasure so that they can keep acquiring spells. The high costs of OD&D magic research actually acts as a balancing mechanism, for those that worry about Fighter/M-U balance. A Fighter's equipment costs a couple hundred gp max, plus a couple gp a month for maintenance; an M-U has to spend a minimum of 2,000 gp just to add one new spell. The cost to get Fireball is 8,000 gp minimum, and that's not even guaranteed; if you absolutely positively have to have it, it will cost 40,000 gp.
Although I like the original approach and it's what I used for the OD&D game I was running earlier this year, I've been thinking of using a system I once proposed for assigning higher-level spells to NPC spellbooks. The benefit of using this technique is that it doesn't require a specially-designed table, like the one in the DMG. Instead, you just use the list in Men & Magic or Greyhawk, whichever you prefer. Also, it's a little more random than the DMG technique and avoids putting too much focus on Read Magic and the popular spells. It has more of a feel of "here's the spells you managed to find or learn from a master." And, of course, there's a minimum of die-rolling; All the dice can be rolled at once, if desired.
In a comment, Brendan asked about my new spell assignment proposal, and since it's not very clear, I thought I'd describe it in more detail. The spell lists in Men & Magic are numbered from 1 to 14 (1 to 18 in Greyhawk,) although not every spell level has that many spells. You can use these numbers to randomly select spells from one of the lists. In the case of 1st level spells, there are exactly eight in M&M, so you could use a d8 to pick one spell, or a d12 if using the Greyhawk list (since there are only 11 spells on the Greyhawk list, just treat a 12 as a 1.)
Roll the appropriate die to select the first spell in the character's spellbook. The M-U knows that spell and the five spells after it, in order. Then, roll a d20 twice to select additional spells from the same list; if the result is greater than 8 (or 11,) there is no additional spell on that roll, but otherwise, you add the indicated spell unless you've already rolled that spell before, in which case you drop the spell. Thus, the M-U will wind up with 4 to 8 spells.